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Chapter 5 Generic Programming
Anshuman RazdanDiv of Computing Studies
razdanasueduhttpdcst2eastasuedu~razdancst230
CET230 -- Razdan et al 2
Javarsquos Object typebull Java has 8 primitive types byte short int
long float double char boolean
bull Everything else is an Object
bull An ADT should be designed so that it can hold anything rather than specific typesndash Eg we made a list that could hold integers ndash
what if we need a list of strings or floats or students (from some Student class)hellip
ndash It would be better to make a list of Objects then we could put anything in the list
CET230 -- Razdan et al 3
Issues for ADT that hold objects
bull Class name should be arbitrary (not tied to a type Eg use Bag not IntBag)
bull Type of the underlying element is Object
bull Equality test should use equals not == or =
bull Decide how to deal with null references ndash can they be elements in the ADT
CET230 -- Razdan et al 4
Widening Conversions
bull If x and y are reference variables x=y is a widening conversion if the data type of x is capable of referring to a wider variety of things than the type of y
bull EgIntBag B = new IntBag()Object objobj = B
bull Java allows all widening conversions
CET230 -- Razdan et al 5
Narrowing Conversions
bull If x and y are reference variables x=y is a narrowing conversion if x has a smaller ability to refer to things than y
bull Eg Object obj = new IntBag()
IntBag B
B = obj
By using a typecast Java will allow all narrowing conversions (a ClassCastException could be thrown if conversion is ldquoillegalrdquo)
CET230 -- Razdan et al 6
Wrapper Classes
bull A wrapper class is a class in which each object holds a primitive classndash Byte Short Integer Long Float Double
Character Boolean are wrapper classesndash Accessor methods xxxValue() where xxx is
primitive type
bull Note Java 15 provides ldquoauto-boxingrdquo which replaces need for Accessor methods
CET230 -- Razdan et al 7
Old vs Newbull Wrappers bull Boxing
ObjList L = new ObjList() must put primitive value 3 into an object (box it) in order to have an object to insert in the listLinsert( new Integer(3) )hellipInteger num = (Integer)LgetHead() now we must ldquoun-boxrdquo the primitive value int i = numintValue()
ObjList L = new ObjList() Java 15 will auto-boxLinsert( 3 )hellip Java 15 will auto-unboxint I = LgetHead()
bullSee httpjavasuncomj2se150docsguidelanguageautoboxinghtmlfor discussion on autoboxing
CET230 -- Razdan et al 8
Clones amp Deep Clonesbull Consider the following codeclass Node implements Cloneable private Object data private Node next
public Object clone() Node nodeClone try nodeClone = (Node) superclone() catch( CloneNotSupportedException e)
CET230 -- Razdan et al 9
Fix (kinda) previousbull The previous example is a ldquoshallowrdquo clone
bull Fix the code to make a deep(er) cloneclass Node implements Cloneable Object data Node next public Object clone() Node nodeClone try nodeClone = (Node) superclone() catch( CloneNotSupportedException e) nodeClonesetData( thisdata )
nodeClonesetNext( )
CET230 -- Razdan et al 10
Really fix the shallow clonebull We still have a problem with the previous code
Nodes hold Object so clones are referencing the same data
bull What wersquod like to do is
bull But this has a problemndash We donrsquot know the actual class that ldquodatardquo belongs to ndash
it might not be Cloneable
bull To fix this check if ldquodatardquo is instanceof Cloneable If so we can do the ldquodeeprdquo clone If not then wersquore stuck with referencing the same ldquodatardquo object
nodeClonesetData(thisgetData()clone())
CET230 -- Razdan et al 11
List clone can use Node clonebull If a Node is Cloneable then the List clone
is pretty easy (all the work is done by the Node)
bull Consider the following (for List clone)
listClonehead = (Node) thisheadclone()
bull Now we just need to set listClonetail How about the followinglistClonetail = (Node) thistailclone()
bull What can we do
CET230 -- Razdan et al 12
Doubly Linked Listbull A doubly linked list allows us to store
references to the next node as well as the previous node
3 2 7 11
headtail
CET230 -- Razdan et al 13
Inheritance
bull A Doubly Linked List ldquois-ardquo List So we should take advantage of the List wersquove already implementedndash DoubleNode extends Nodendash DoubleList extends List
CET230 -- Razdan et al 14
Other Lists
bull Other types of lists are usefulndash Ordered list (elements in list are stored in some
order) Eg numbers are in increasing order strings are in alphabetical order etc
ndash Circular List the ldquoendrdquo of the list refers back to the head
ndash Skip Lists
CET230 -- Razdan et al 15
SkipList example from httpepaperpresscom
CET230 -- Razdan et al 16
Abstract Classesbull A robust implementation for List is to have an
ldquoAbstractListrdquo class from which concrete Lists (Singly Linked Doubly Linked Ordered etc) can be derived
bull An abstract classndash Has at least one abstract method (a method whose
interface is defined but NO implementation is specified by the class)
ndash Cannot be instantiatedndash Can provide implementation for some methodsndash Can provide attributes common to all concrete
subclasses
CET230 -- Razdan et al 17
Abstract List
bull Attributesndash head tail length
bull Methodsndash Constructor getLength equals clone
bull Abstract Methodsndash Add remove clone
CET230 -- Razdan et al 18
Implement clone in AbstractList
bull What Irsquod really like is to implement the clone() in the AbstractList classndash All Lists contain Nodes We donrsquot want to
rewrite the same code for the clone method over and over again in the concrete List classes
ndash Problem what about a DoubleList that contains DoubleNode The AbstractList implementation will not do enoughbecause the Node clone does not do enough
ndash But I WANT it to do enough
CET230 -- Razdan et al 19
Reflectionbull What if we made the Node clone ldquosmarterrdquo
ndash if itrsquos just a Node then do a Node clonendash if itrsquos some other kind of Node then do that
clonendash But the Node doesnrsquot know all the other classes
that extend it
bull Reflection can be used to obtain information about a class its members or its methods
CET230 -- Razdan et al 20
Reflection cont
bull The Class class (see javalang) has methods that enable us to get information about the classndash eg getMethod(String name Class
[] parameterTypes) returns ldquoMethodrdquo
bull The Method class (see javalangreflect) has methods that enable us to get information about the Method and even CALL the methodndash Object invoke(Object obj Object[] args)
CET230 -- Razdan et al 21
ldquoBionicrdquo Nodebull We can modify the Node clone as follows
Node nodeClonetry nodeClone = (Node) superclone() catch( CloneNotSupportedException e ) throw new CloneNotSupportedException()if( thisdata instanceof Cloneable ) try Class c = thisdatagetClass() Method m = cgetMethod( clone null )
nodeClonedata = minvoke( thisdata null ) catch( Exception e ) nodeClonedata = thisdata else nodeClonedata = thisdataif( thisnext = null ) nodeClonenext = (Node) thisnextclone()else nodeClonenext = nullreturn( nodeClone )
CET230 -- Razdan et al 22
Revisiting the String classbull Some useful String methods
ndash charAt( int index)
ndash indexOf( char ch )
ndash indexOf( String str )
ndash split( String regex )
ndash startsWith( String prefix )
ndash substring( int beginIndex int endIndex )
ndash toLowerCase()
ndash toUpperCase()
Note StringTokenizer is a legacy class that is retained for compatibility reasons although its use is discouraged in new code It is recommended that anyone seeking this functionality use the split method of String or the javautilregex package instead
CET230 -- Razdan et al 23
Using Files for IObull Using files for IO is similar to standard IObull For standard input you usually use
ndash InputStreamReaderndash BufferedReader
bull For standard output you usually usendash Systemoutprint or println
bull For file input you can usendash FileReaderndash BufferedReader
bull For file output you can usendash FileWriterndash BufferedWriter
CET230 -- Razdan et al 24
FileReader constructorFileReader
public FileReader(String fileName) throws FileNotFoundException
Creates a new FileReader given the name of the file to read from
Parameters fileName - the name of the file to read from
Throws FileNotFoundException - if the named file does not exist is a directory rather than a regular file or for some other reason cannot be opened for reading
CET230 -- Razdan et al 25
Read ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )
String s = inreadLine()int i = 1while( s = null )
Systemoutprintln(ldquoLine ldquo + i + ldquo ldquo + s )
i++s = inreadLine()
inclose()
CET230 -- Razdan et al 26
FileWriter constructor
FileWriter
public FileWriter(String fileName) throws IOException Constructs a FileWriter object given a file name
Parameters fileName - String The system-dependent filename
Throws IOException - if the named file exists but is a directory rather than a regular file does not exist but cannot be created or cannot be opened for any other reason
CET230 -- Razdan et al 27
BufferedWriter
Method Summary void
close() Close the stream
voidflush() Flush the stream
voidnewLine() Write a line separator
voidwrite(char[] cbuf int off int len) Write a portion of an array of characters
voidwrite(int c) Write a single character
voidwrite(String s int off int len) Write a portion of a String
CET230 -- Razdan et al 28
Write ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )BufferedWriter out = new BufferedWriter(
new FileWriter(outfile) )
String s = inreadLine()while( s = null )
outwrite((ssplit(ldquosrdquo))[0])outnewLine()s = inreadLine()
inclose()outclose()
CET230 -- Razdan et al 29
Java Interfaces
bull A Java interface is a set of related methods that a programmer may want to support in a single classndash Eg Cloneablendash Eg Comparablehttpjavasuncomj2se150docsapijavalangComparablehtml
CET230 -- Razdan et al 30
Iterator Pattern
bull Motivation ndash an aggregate object should give you a way to access its
elements without exposing its internal structure
ndash Use of the object may want to traverse the object in many different ways ndash donrsquot want to bloat the interface with may traversal methods even if you could anticipate all the methods needed
ndash May need to have more than one traversal pending on the aggregate at once
CET230 -- Razdan et al 31
Iterator Patternbull Key idea take responsibility for access and
traversal out of the object and put it into an iterator object
bull Iterator provides basic ldquonavigationrdquo methods eg ndash Firstndash Nextndash IsDonendash CurrentItem
CET230 -- Razdan et al 32
Map Interface
bull A map is a collection class in which keyvalue pairs may be added A pair can be retrieved or removed by specifying just its key
CET230 -- Razdan et al 33
TreeMap
bull Javarsquos TreeMapltK Vgt implements the map interface in an efficient way in which the keys are required to come from a class (such as String) that implements the Comparable interface
CET230 -- Razdan et al 34
Example
bull From package javautil
bull TreeMapltString Integergt frequencyData
bull String word
bull Integer count
CET230 -- Razdan et al 35
Operations
bull public V get(K key)
bull public V put(K key V value)
bull public boolean containsKey(K key)
bull public SetltKgt keySet()
bull public int size()
bull public void clear()
CET230 -- Razdan et al 36
Iteration
for (String word wordMapkeySet())
hellipprocess this key which is in variable wordhellip
CET230 -- Razdan et al 2
Javarsquos Object typebull Java has 8 primitive types byte short int
long float double char boolean
bull Everything else is an Object
bull An ADT should be designed so that it can hold anything rather than specific typesndash Eg we made a list that could hold integers ndash
what if we need a list of strings or floats or students (from some Student class)hellip
ndash It would be better to make a list of Objects then we could put anything in the list
CET230 -- Razdan et al 3
Issues for ADT that hold objects
bull Class name should be arbitrary (not tied to a type Eg use Bag not IntBag)
bull Type of the underlying element is Object
bull Equality test should use equals not == or =
bull Decide how to deal with null references ndash can they be elements in the ADT
CET230 -- Razdan et al 4
Widening Conversions
bull If x and y are reference variables x=y is a widening conversion if the data type of x is capable of referring to a wider variety of things than the type of y
bull EgIntBag B = new IntBag()Object objobj = B
bull Java allows all widening conversions
CET230 -- Razdan et al 5
Narrowing Conversions
bull If x and y are reference variables x=y is a narrowing conversion if x has a smaller ability to refer to things than y
bull Eg Object obj = new IntBag()
IntBag B
B = obj
By using a typecast Java will allow all narrowing conversions (a ClassCastException could be thrown if conversion is ldquoillegalrdquo)
CET230 -- Razdan et al 6
Wrapper Classes
bull A wrapper class is a class in which each object holds a primitive classndash Byte Short Integer Long Float Double
Character Boolean are wrapper classesndash Accessor methods xxxValue() where xxx is
primitive type
bull Note Java 15 provides ldquoauto-boxingrdquo which replaces need for Accessor methods
CET230 -- Razdan et al 7
Old vs Newbull Wrappers bull Boxing
ObjList L = new ObjList() must put primitive value 3 into an object (box it) in order to have an object to insert in the listLinsert( new Integer(3) )hellipInteger num = (Integer)LgetHead() now we must ldquoun-boxrdquo the primitive value int i = numintValue()
ObjList L = new ObjList() Java 15 will auto-boxLinsert( 3 )hellip Java 15 will auto-unboxint I = LgetHead()
bullSee httpjavasuncomj2se150docsguidelanguageautoboxinghtmlfor discussion on autoboxing
CET230 -- Razdan et al 8
Clones amp Deep Clonesbull Consider the following codeclass Node implements Cloneable private Object data private Node next
public Object clone() Node nodeClone try nodeClone = (Node) superclone() catch( CloneNotSupportedException e)
CET230 -- Razdan et al 9
Fix (kinda) previousbull The previous example is a ldquoshallowrdquo clone
bull Fix the code to make a deep(er) cloneclass Node implements Cloneable Object data Node next public Object clone() Node nodeClone try nodeClone = (Node) superclone() catch( CloneNotSupportedException e) nodeClonesetData( thisdata )
nodeClonesetNext( )
CET230 -- Razdan et al 10
Really fix the shallow clonebull We still have a problem with the previous code
Nodes hold Object so clones are referencing the same data
bull What wersquod like to do is
bull But this has a problemndash We donrsquot know the actual class that ldquodatardquo belongs to ndash
it might not be Cloneable
bull To fix this check if ldquodatardquo is instanceof Cloneable If so we can do the ldquodeeprdquo clone If not then wersquore stuck with referencing the same ldquodatardquo object
nodeClonesetData(thisgetData()clone())
CET230 -- Razdan et al 11
List clone can use Node clonebull If a Node is Cloneable then the List clone
is pretty easy (all the work is done by the Node)
bull Consider the following (for List clone)
listClonehead = (Node) thisheadclone()
bull Now we just need to set listClonetail How about the followinglistClonetail = (Node) thistailclone()
bull What can we do
CET230 -- Razdan et al 12
Doubly Linked Listbull A doubly linked list allows us to store
references to the next node as well as the previous node
3 2 7 11
headtail
CET230 -- Razdan et al 13
Inheritance
bull A Doubly Linked List ldquois-ardquo List So we should take advantage of the List wersquove already implementedndash DoubleNode extends Nodendash DoubleList extends List
CET230 -- Razdan et al 14
Other Lists
bull Other types of lists are usefulndash Ordered list (elements in list are stored in some
order) Eg numbers are in increasing order strings are in alphabetical order etc
ndash Circular List the ldquoendrdquo of the list refers back to the head
ndash Skip Lists
CET230 -- Razdan et al 15
SkipList example from httpepaperpresscom
CET230 -- Razdan et al 16
Abstract Classesbull A robust implementation for List is to have an
ldquoAbstractListrdquo class from which concrete Lists (Singly Linked Doubly Linked Ordered etc) can be derived
bull An abstract classndash Has at least one abstract method (a method whose
interface is defined but NO implementation is specified by the class)
ndash Cannot be instantiatedndash Can provide implementation for some methodsndash Can provide attributes common to all concrete
subclasses
CET230 -- Razdan et al 17
Abstract List
bull Attributesndash head tail length
bull Methodsndash Constructor getLength equals clone
bull Abstract Methodsndash Add remove clone
CET230 -- Razdan et al 18
Implement clone in AbstractList
bull What Irsquod really like is to implement the clone() in the AbstractList classndash All Lists contain Nodes We donrsquot want to
rewrite the same code for the clone method over and over again in the concrete List classes
ndash Problem what about a DoubleList that contains DoubleNode The AbstractList implementation will not do enoughbecause the Node clone does not do enough
ndash But I WANT it to do enough
CET230 -- Razdan et al 19
Reflectionbull What if we made the Node clone ldquosmarterrdquo
ndash if itrsquos just a Node then do a Node clonendash if itrsquos some other kind of Node then do that
clonendash But the Node doesnrsquot know all the other classes
that extend it
bull Reflection can be used to obtain information about a class its members or its methods
CET230 -- Razdan et al 20
Reflection cont
bull The Class class (see javalang) has methods that enable us to get information about the classndash eg getMethod(String name Class
[] parameterTypes) returns ldquoMethodrdquo
bull The Method class (see javalangreflect) has methods that enable us to get information about the Method and even CALL the methodndash Object invoke(Object obj Object[] args)
CET230 -- Razdan et al 21
ldquoBionicrdquo Nodebull We can modify the Node clone as follows
Node nodeClonetry nodeClone = (Node) superclone() catch( CloneNotSupportedException e ) throw new CloneNotSupportedException()if( thisdata instanceof Cloneable ) try Class c = thisdatagetClass() Method m = cgetMethod( clone null )
nodeClonedata = minvoke( thisdata null ) catch( Exception e ) nodeClonedata = thisdata else nodeClonedata = thisdataif( thisnext = null ) nodeClonenext = (Node) thisnextclone()else nodeClonenext = nullreturn( nodeClone )
CET230 -- Razdan et al 22
Revisiting the String classbull Some useful String methods
ndash charAt( int index)
ndash indexOf( char ch )
ndash indexOf( String str )
ndash split( String regex )
ndash startsWith( String prefix )
ndash substring( int beginIndex int endIndex )
ndash toLowerCase()
ndash toUpperCase()
Note StringTokenizer is a legacy class that is retained for compatibility reasons although its use is discouraged in new code It is recommended that anyone seeking this functionality use the split method of String or the javautilregex package instead
CET230 -- Razdan et al 23
Using Files for IObull Using files for IO is similar to standard IObull For standard input you usually use
ndash InputStreamReaderndash BufferedReader
bull For standard output you usually usendash Systemoutprint or println
bull For file input you can usendash FileReaderndash BufferedReader
bull For file output you can usendash FileWriterndash BufferedWriter
CET230 -- Razdan et al 24
FileReader constructorFileReader
public FileReader(String fileName) throws FileNotFoundException
Creates a new FileReader given the name of the file to read from
Parameters fileName - the name of the file to read from
Throws FileNotFoundException - if the named file does not exist is a directory rather than a regular file or for some other reason cannot be opened for reading
CET230 -- Razdan et al 25
Read ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )
String s = inreadLine()int i = 1while( s = null )
Systemoutprintln(ldquoLine ldquo + i + ldquo ldquo + s )
i++s = inreadLine()
inclose()
CET230 -- Razdan et al 26
FileWriter constructor
FileWriter
public FileWriter(String fileName) throws IOException Constructs a FileWriter object given a file name
Parameters fileName - String The system-dependent filename
Throws IOException - if the named file exists but is a directory rather than a regular file does not exist but cannot be created or cannot be opened for any other reason
CET230 -- Razdan et al 27
BufferedWriter
Method Summary void
close() Close the stream
voidflush() Flush the stream
voidnewLine() Write a line separator
voidwrite(char[] cbuf int off int len) Write a portion of an array of characters
voidwrite(int c) Write a single character
voidwrite(String s int off int len) Write a portion of a String
CET230 -- Razdan et al 28
Write ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )BufferedWriter out = new BufferedWriter(
new FileWriter(outfile) )
String s = inreadLine()while( s = null )
outwrite((ssplit(ldquosrdquo))[0])outnewLine()s = inreadLine()
inclose()outclose()
CET230 -- Razdan et al 29
Java Interfaces
bull A Java interface is a set of related methods that a programmer may want to support in a single classndash Eg Cloneablendash Eg Comparablehttpjavasuncomj2se150docsapijavalangComparablehtml
CET230 -- Razdan et al 30
Iterator Pattern
bull Motivation ndash an aggregate object should give you a way to access its
elements without exposing its internal structure
ndash Use of the object may want to traverse the object in many different ways ndash donrsquot want to bloat the interface with may traversal methods even if you could anticipate all the methods needed
ndash May need to have more than one traversal pending on the aggregate at once
CET230 -- Razdan et al 31
Iterator Patternbull Key idea take responsibility for access and
traversal out of the object and put it into an iterator object
bull Iterator provides basic ldquonavigationrdquo methods eg ndash Firstndash Nextndash IsDonendash CurrentItem
CET230 -- Razdan et al 32
Map Interface
bull A map is a collection class in which keyvalue pairs may be added A pair can be retrieved or removed by specifying just its key
CET230 -- Razdan et al 33
TreeMap
bull Javarsquos TreeMapltK Vgt implements the map interface in an efficient way in which the keys are required to come from a class (such as String) that implements the Comparable interface
CET230 -- Razdan et al 34
Example
bull From package javautil
bull TreeMapltString Integergt frequencyData
bull String word
bull Integer count
CET230 -- Razdan et al 35
Operations
bull public V get(K key)
bull public V put(K key V value)
bull public boolean containsKey(K key)
bull public SetltKgt keySet()
bull public int size()
bull public void clear()
CET230 -- Razdan et al 36
Iteration
for (String word wordMapkeySet())
hellipprocess this key which is in variable wordhellip
CET230 -- Razdan et al 3
Issues for ADT that hold objects
bull Class name should be arbitrary (not tied to a type Eg use Bag not IntBag)
bull Type of the underlying element is Object
bull Equality test should use equals not == or =
bull Decide how to deal with null references ndash can they be elements in the ADT
CET230 -- Razdan et al 4
Widening Conversions
bull If x and y are reference variables x=y is a widening conversion if the data type of x is capable of referring to a wider variety of things than the type of y
bull EgIntBag B = new IntBag()Object objobj = B
bull Java allows all widening conversions
CET230 -- Razdan et al 5
Narrowing Conversions
bull If x and y are reference variables x=y is a narrowing conversion if x has a smaller ability to refer to things than y
bull Eg Object obj = new IntBag()
IntBag B
B = obj
By using a typecast Java will allow all narrowing conversions (a ClassCastException could be thrown if conversion is ldquoillegalrdquo)
CET230 -- Razdan et al 6
Wrapper Classes
bull A wrapper class is a class in which each object holds a primitive classndash Byte Short Integer Long Float Double
Character Boolean are wrapper classesndash Accessor methods xxxValue() where xxx is
primitive type
bull Note Java 15 provides ldquoauto-boxingrdquo which replaces need for Accessor methods
CET230 -- Razdan et al 7
Old vs Newbull Wrappers bull Boxing
ObjList L = new ObjList() must put primitive value 3 into an object (box it) in order to have an object to insert in the listLinsert( new Integer(3) )hellipInteger num = (Integer)LgetHead() now we must ldquoun-boxrdquo the primitive value int i = numintValue()
ObjList L = new ObjList() Java 15 will auto-boxLinsert( 3 )hellip Java 15 will auto-unboxint I = LgetHead()
bullSee httpjavasuncomj2se150docsguidelanguageautoboxinghtmlfor discussion on autoboxing
CET230 -- Razdan et al 8
Clones amp Deep Clonesbull Consider the following codeclass Node implements Cloneable private Object data private Node next
public Object clone() Node nodeClone try nodeClone = (Node) superclone() catch( CloneNotSupportedException e)
CET230 -- Razdan et al 9
Fix (kinda) previousbull The previous example is a ldquoshallowrdquo clone
bull Fix the code to make a deep(er) cloneclass Node implements Cloneable Object data Node next public Object clone() Node nodeClone try nodeClone = (Node) superclone() catch( CloneNotSupportedException e) nodeClonesetData( thisdata )
nodeClonesetNext( )
CET230 -- Razdan et al 10
Really fix the shallow clonebull We still have a problem with the previous code
Nodes hold Object so clones are referencing the same data
bull What wersquod like to do is
bull But this has a problemndash We donrsquot know the actual class that ldquodatardquo belongs to ndash
it might not be Cloneable
bull To fix this check if ldquodatardquo is instanceof Cloneable If so we can do the ldquodeeprdquo clone If not then wersquore stuck with referencing the same ldquodatardquo object
nodeClonesetData(thisgetData()clone())
CET230 -- Razdan et al 11
List clone can use Node clonebull If a Node is Cloneable then the List clone
is pretty easy (all the work is done by the Node)
bull Consider the following (for List clone)
listClonehead = (Node) thisheadclone()
bull Now we just need to set listClonetail How about the followinglistClonetail = (Node) thistailclone()
bull What can we do
CET230 -- Razdan et al 12
Doubly Linked Listbull A doubly linked list allows us to store
references to the next node as well as the previous node
3 2 7 11
headtail
CET230 -- Razdan et al 13
Inheritance
bull A Doubly Linked List ldquois-ardquo List So we should take advantage of the List wersquove already implementedndash DoubleNode extends Nodendash DoubleList extends List
CET230 -- Razdan et al 14
Other Lists
bull Other types of lists are usefulndash Ordered list (elements in list are stored in some
order) Eg numbers are in increasing order strings are in alphabetical order etc
ndash Circular List the ldquoendrdquo of the list refers back to the head
ndash Skip Lists
CET230 -- Razdan et al 15
SkipList example from httpepaperpresscom
CET230 -- Razdan et al 16
Abstract Classesbull A robust implementation for List is to have an
ldquoAbstractListrdquo class from which concrete Lists (Singly Linked Doubly Linked Ordered etc) can be derived
bull An abstract classndash Has at least one abstract method (a method whose
interface is defined but NO implementation is specified by the class)
ndash Cannot be instantiatedndash Can provide implementation for some methodsndash Can provide attributes common to all concrete
subclasses
CET230 -- Razdan et al 17
Abstract List
bull Attributesndash head tail length
bull Methodsndash Constructor getLength equals clone
bull Abstract Methodsndash Add remove clone
CET230 -- Razdan et al 18
Implement clone in AbstractList
bull What Irsquod really like is to implement the clone() in the AbstractList classndash All Lists contain Nodes We donrsquot want to
rewrite the same code for the clone method over and over again in the concrete List classes
ndash Problem what about a DoubleList that contains DoubleNode The AbstractList implementation will not do enoughbecause the Node clone does not do enough
ndash But I WANT it to do enough
CET230 -- Razdan et al 19
Reflectionbull What if we made the Node clone ldquosmarterrdquo
ndash if itrsquos just a Node then do a Node clonendash if itrsquos some other kind of Node then do that
clonendash But the Node doesnrsquot know all the other classes
that extend it
bull Reflection can be used to obtain information about a class its members or its methods
CET230 -- Razdan et al 20
Reflection cont
bull The Class class (see javalang) has methods that enable us to get information about the classndash eg getMethod(String name Class
[] parameterTypes) returns ldquoMethodrdquo
bull The Method class (see javalangreflect) has methods that enable us to get information about the Method and even CALL the methodndash Object invoke(Object obj Object[] args)
CET230 -- Razdan et al 21
ldquoBionicrdquo Nodebull We can modify the Node clone as follows
Node nodeClonetry nodeClone = (Node) superclone() catch( CloneNotSupportedException e ) throw new CloneNotSupportedException()if( thisdata instanceof Cloneable ) try Class c = thisdatagetClass() Method m = cgetMethod( clone null )
nodeClonedata = minvoke( thisdata null ) catch( Exception e ) nodeClonedata = thisdata else nodeClonedata = thisdataif( thisnext = null ) nodeClonenext = (Node) thisnextclone()else nodeClonenext = nullreturn( nodeClone )
CET230 -- Razdan et al 22
Revisiting the String classbull Some useful String methods
ndash charAt( int index)
ndash indexOf( char ch )
ndash indexOf( String str )
ndash split( String regex )
ndash startsWith( String prefix )
ndash substring( int beginIndex int endIndex )
ndash toLowerCase()
ndash toUpperCase()
Note StringTokenizer is a legacy class that is retained for compatibility reasons although its use is discouraged in new code It is recommended that anyone seeking this functionality use the split method of String or the javautilregex package instead
CET230 -- Razdan et al 23
Using Files for IObull Using files for IO is similar to standard IObull For standard input you usually use
ndash InputStreamReaderndash BufferedReader
bull For standard output you usually usendash Systemoutprint or println
bull For file input you can usendash FileReaderndash BufferedReader
bull For file output you can usendash FileWriterndash BufferedWriter
CET230 -- Razdan et al 24
FileReader constructorFileReader
public FileReader(String fileName) throws FileNotFoundException
Creates a new FileReader given the name of the file to read from
Parameters fileName - the name of the file to read from
Throws FileNotFoundException - if the named file does not exist is a directory rather than a regular file or for some other reason cannot be opened for reading
CET230 -- Razdan et al 25
Read ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )
String s = inreadLine()int i = 1while( s = null )
Systemoutprintln(ldquoLine ldquo + i + ldquo ldquo + s )
i++s = inreadLine()
inclose()
CET230 -- Razdan et al 26
FileWriter constructor
FileWriter
public FileWriter(String fileName) throws IOException Constructs a FileWriter object given a file name
Parameters fileName - String The system-dependent filename
Throws IOException - if the named file exists but is a directory rather than a regular file does not exist but cannot be created or cannot be opened for any other reason
CET230 -- Razdan et al 27
BufferedWriter
Method Summary void
close() Close the stream
voidflush() Flush the stream
voidnewLine() Write a line separator
voidwrite(char[] cbuf int off int len) Write a portion of an array of characters
voidwrite(int c) Write a single character
voidwrite(String s int off int len) Write a portion of a String
CET230 -- Razdan et al 28
Write ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )BufferedWriter out = new BufferedWriter(
new FileWriter(outfile) )
String s = inreadLine()while( s = null )
outwrite((ssplit(ldquosrdquo))[0])outnewLine()s = inreadLine()
inclose()outclose()
CET230 -- Razdan et al 29
Java Interfaces
bull A Java interface is a set of related methods that a programmer may want to support in a single classndash Eg Cloneablendash Eg Comparablehttpjavasuncomj2se150docsapijavalangComparablehtml
CET230 -- Razdan et al 30
Iterator Pattern
bull Motivation ndash an aggregate object should give you a way to access its
elements without exposing its internal structure
ndash Use of the object may want to traverse the object in many different ways ndash donrsquot want to bloat the interface with may traversal methods even if you could anticipate all the methods needed
ndash May need to have more than one traversal pending on the aggregate at once
CET230 -- Razdan et al 31
Iterator Patternbull Key idea take responsibility for access and
traversal out of the object and put it into an iterator object
bull Iterator provides basic ldquonavigationrdquo methods eg ndash Firstndash Nextndash IsDonendash CurrentItem
CET230 -- Razdan et al 32
Map Interface
bull A map is a collection class in which keyvalue pairs may be added A pair can be retrieved or removed by specifying just its key
CET230 -- Razdan et al 33
TreeMap
bull Javarsquos TreeMapltK Vgt implements the map interface in an efficient way in which the keys are required to come from a class (such as String) that implements the Comparable interface
CET230 -- Razdan et al 34
Example
bull From package javautil
bull TreeMapltString Integergt frequencyData
bull String word
bull Integer count
CET230 -- Razdan et al 35
Operations
bull public V get(K key)
bull public V put(K key V value)
bull public boolean containsKey(K key)
bull public SetltKgt keySet()
bull public int size()
bull public void clear()
CET230 -- Razdan et al 36
Iteration
for (String word wordMapkeySet())
hellipprocess this key which is in variable wordhellip
CET230 -- Razdan et al 4
Widening Conversions
bull If x and y are reference variables x=y is a widening conversion if the data type of x is capable of referring to a wider variety of things than the type of y
bull EgIntBag B = new IntBag()Object objobj = B
bull Java allows all widening conversions
CET230 -- Razdan et al 5
Narrowing Conversions
bull If x and y are reference variables x=y is a narrowing conversion if x has a smaller ability to refer to things than y
bull Eg Object obj = new IntBag()
IntBag B
B = obj
By using a typecast Java will allow all narrowing conversions (a ClassCastException could be thrown if conversion is ldquoillegalrdquo)
CET230 -- Razdan et al 6
Wrapper Classes
bull A wrapper class is a class in which each object holds a primitive classndash Byte Short Integer Long Float Double
Character Boolean are wrapper classesndash Accessor methods xxxValue() where xxx is
primitive type
bull Note Java 15 provides ldquoauto-boxingrdquo which replaces need for Accessor methods
CET230 -- Razdan et al 7
Old vs Newbull Wrappers bull Boxing
ObjList L = new ObjList() must put primitive value 3 into an object (box it) in order to have an object to insert in the listLinsert( new Integer(3) )hellipInteger num = (Integer)LgetHead() now we must ldquoun-boxrdquo the primitive value int i = numintValue()
ObjList L = new ObjList() Java 15 will auto-boxLinsert( 3 )hellip Java 15 will auto-unboxint I = LgetHead()
bullSee httpjavasuncomj2se150docsguidelanguageautoboxinghtmlfor discussion on autoboxing
CET230 -- Razdan et al 8
Clones amp Deep Clonesbull Consider the following codeclass Node implements Cloneable private Object data private Node next
public Object clone() Node nodeClone try nodeClone = (Node) superclone() catch( CloneNotSupportedException e)
CET230 -- Razdan et al 9
Fix (kinda) previousbull The previous example is a ldquoshallowrdquo clone
bull Fix the code to make a deep(er) cloneclass Node implements Cloneable Object data Node next public Object clone() Node nodeClone try nodeClone = (Node) superclone() catch( CloneNotSupportedException e) nodeClonesetData( thisdata )
nodeClonesetNext( )
CET230 -- Razdan et al 10
Really fix the shallow clonebull We still have a problem with the previous code
Nodes hold Object so clones are referencing the same data
bull What wersquod like to do is
bull But this has a problemndash We donrsquot know the actual class that ldquodatardquo belongs to ndash
it might not be Cloneable
bull To fix this check if ldquodatardquo is instanceof Cloneable If so we can do the ldquodeeprdquo clone If not then wersquore stuck with referencing the same ldquodatardquo object
nodeClonesetData(thisgetData()clone())
CET230 -- Razdan et al 11
List clone can use Node clonebull If a Node is Cloneable then the List clone
is pretty easy (all the work is done by the Node)
bull Consider the following (for List clone)
listClonehead = (Node) thisheadclone()
bull Now we just need to set listClonetail How about the followinglistClonetail = (Node) thistailclone()
bull What can we do
CET230 -- Razdan et al 12
Doubly Linked Listbull A doubly linked list allows us to store
references to the next node as well as the previous node
3 2 7 11
headtail
CET230 -- Razdan et al 13
Inheritance
bull A Doubly Linked List ldquois-ardquo List So we should take advantage of the List wersquove already implementedndash DoubleNode extends Nodendash DoubleList extends List
CET230 -- Razdan et al 14
Other Lists
bull Other types of lists are usefulndash Ordered list (elements in list are stored in some
order) Eg numbers are in increasing order strings are in alphabetical order etc
ndash Circular List the ldquoendrdquo of the list refers back to the head
ndash Skip Lists
CET230 -- Razdan et al 15
SkipList example from httpepaperpresscom
CET230 -- Razdan et al 16
Abstract Classesbull A robust implementation for List is to have an
ldquoAbstractListrdquo class from which concrete Lists (Singly Linked Doubly Linked Ordered etc) can be derived
bull An abstract classndash Has at least one abstract method (a method whose
interface is defined but NO implementation is specified by the class)
ndash Cannot be instantiatedndash Can provide implementation for some methodsndash Can provide attributes common to all concrete
subclasses
CET230 -- Razdan et al 17
Abstract List
bull Attributesndash head tail length
bull Methodsndash Constructor getLength equals clone
bull Abstract Methodsndash Add remove clone
CET230 -- Razdan et al 18
Implement clone in AbstractList
bull What Irsquod really like is to implement the clone() in the AbstractList classndash All Lists contain Nodes We donrsquot want to
rewrite the same code for the clone method over and over again in the concrete List classes
ndash Problem what about a DoubleList that contains DoubleNode The AbstractList implementation will not do enoughbecause the Node clone does not do enough
ndash But I WANT it to do enough
CET230 -- Razdan et al 19
Reflectionbull What if we made the Node clone ldquosmarterrdquo
ndash if itrsquos just a Node then do a Node clonendash if itrsquos some other kind of Node then do that
clonendash But the Node doesnrsquot know all the other classes
that extend it
bull Reflection can be used to obtain information about a class its members or its methods
CET230 -- Razdan et al 20
Reflection cont
bull The Class class (see javalang) has methods that enable us to get information about the classndash eg getMethod(String name Class
[] parameterTypes) returns ldquoMethodrdquo
bull The Method class (see javalangreflect) has methods that enable us to get information about the Method and even CALL the methodndash Object invoke(Object obj Object[] args)
CET230 -- Razdan et al 21
ldquoBionicrdquo Nodebull We can modify the Node clone as follows
Node nodeClonetry nodeClone = (Node) superclone() catch( CloneNotSupportedException e ) throw new CloneNotSupportedException()if( thisdata instanceof Cloneable ) try Class c = thisdatagetClass() Method m = cgetMethod( clone null )
nodeClonedata = minvoke( thisdata null ) catch( Exception e ) nodeClonedata = thisdata else nodeClonedata = thisdataif( thisnext = null ) nodeClonenext = (Node) thisnextclone()else nodeClonenext = nullreturn( nodeClone )
CET230 -- Razdan et al 22
Revisiting the String classbull Some useful String methods
ndash charAt( int index)
ndash indexOf( char ch )
ndash indexOf( String str )
ndash split( String regex )
ndash startsWith( String prefix )
ndash substring( int beginIndex int endIndex )
ndash toLowerCase()
ndash toUpperCase()
Note StringTokenizer is a legacy class that is retained for compatibility reasons although its use is discouraged in new code It is recommended that anyone seeking this functionality use the split method of String or the javautilregex package instead
CET230 -- Razdan et al 23
Using Files for IObull Using files for IO is similar to standard IObull For standard input you usually use
ndash InputStreamReaderndash BufferedReader
bull For standard output you usually usendash Systemoutprint or println
bull For file input you can usendash FileReaderndash BufferedReader
bull For file output you can usendash FileWriterndash BufferedWriter
CET230 -- Razdan et al 24
FileReader constructorFileReader
public FileReader(String fileName) throws FileNotFoundException
Creates a new FileReader given the name of the file to read from
Parameters fileName - the name of the file to read from
Throws FileNotFoundException - if the named file does not exist is a directory rather than a regular file or for some other reason cannot be opened for reading
CET230 -- Razdan et al 25
Read ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )
String s = inreadLine()int i = 1while( s = null )
Systemoutprintln(ldquoLine ldquo + i + ldquo ldquo + s )
i++s = inreadLine()
inclose()
CET230 -- Razdan et al 26
FileWriter constructor
FileWriter
public FileWriter(String fileName) throws IOException Constructs a FileWriter object given a file name
Parameters fileName - String The system-dependent filename
Throws IOException - if the named file exists but is a directory rather than a regular file does not exist but cannot be created or cannot be opened for any other reason
CET230 -- Razdan et al 27
BufferedWriter
Method Summary void
close() Close the stream
voidflush() Flush the stream
voidnewLine() Write a line separator
voidwrite(char[] cbuf int off int len) Write a portion of an array of characters
voidwrite(int c) Write a single character
voidwrite(String s int off int len) Write a portion of a String
CET230 -- Razdan et al 28
Write ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )BufferedWriter out = new BufferedWriter(
new FileWriter(outfile) )
String s = inreadLine()while( s = null )
outwrite((ssplit(ldquosrdquo))[0])outnewLine()s = inreadLine()
inclose()outclose()
CET230 -- Razdan et al 29
Java Interfaces
bull A Java interface is a set of related methods that a programmer may want to support in a single classndash Eg Cloneablendash Eg Comparablehttpjavasuncomj2se150docsapijavalangComparablehtml
CET230 -- Razdan et al 30
Iterator Pattern
bull Motivation ndash an aggregate object should give you a way to access its
elements without exposing its internal structure
ndash Use of the object may want to traverse the object in many different ways ndash donrsquot want to bloat the interface with may traversal methods even if you could anticipate all the methods needed
ndash May need to have more than one traversal pending on the aggregate at once
CET230 -- Razdan et al 31
Iterator Patternbull Key idea take responsibility for access and
traversal out of the object and put it into an iterator object
bull Iterator provides basic ldquonavigationrdquo methods eg ndash Firstndash Nextndash IsDonendash CurrentItem
CET230 -- Razdan et al 32
Map Interface
bull A map is a collection class in which keyvalue pairs may be added A pair can be retrieved or removed by specifying just its key
CET230 -- Razdan et al 33
TreeMap
bull Javarsquos TreeMapltK Vgt implements the map interface in an efficient way in which the keys are required to come from a class (such as String) that implements the Comparable interface
CET230 -- Razdan et al 34
Example
bull From package javautil
bull TreeMapltString Integergt frequencyData
bull String word
bull Integer count
CET230 -- Razdan et al 35
Operations
bull public V get(K key)
bull public V put(K key V value)
bull public boolean containsKey(K key)
bull public SetltKgt keySet()
bull public int size()
bull public void clear()
CET230 -- Razdan et al 36
Iteration
for (String word wordMapkeySet())
hellipprocess this key which is in variable wordhellip
CET230 -- Razdan et al 5
Narrowing Conversions
bull If x and y are reference variables x=y is a narrowing conversion if x has a smaller ability to refer to things than y
bull Eg Object obj = new IntBag()
IntBag B
B = obj
By using a typecast Java will allow all narrowing conversions (a ClassCastException could be thrown if conversion is ldquoillegalrdquo)
CET230 -- Razdan et al 6
Wrapper Classes
bull A wrapper class is a class in which each object holds a primitive classndash Byte Short Integer Long Float Double
Character Boolean are wrapper classesndash Accessor methods xxxValue() where xxx is
primitive type
bull Note Java 15 provides ldquoauto-boxingrdquo which replaces need for Accessor methods
CET230 -- Razdan et al 7
Old vs Newbull Wrappers bull Boxing
ObjList L = new ObjList() must put primitive value 3 into an object (box it) in order to have an object to insert in the listLinsert( new Integer(3) )hellipInteger num = (Integer)LgetHead() now we must ldquoun-boxrdquo the primitive value int i = numintValue()
ObjList L = new ObjList() Java 15 will auto-boxLinsert( 3 )hellip Java 15 will auto-unboxint I = LgetHead()
bullSee httpjavasuncomj2se150docsguidelanguageautoboxinghtmlfor discussion on autoboxing
CET230 -- Razdan et al 8
Clones amp Deep Clonesbull Consider the following codeclass Node implements Cloneable private Object data private Node next
public Object clone() Node nodeClone try nodeClone = (Node) superclone() catch( CloneNotSupportedException e)
CET230 -- Razdan et al 9
Fix (kinda) previousbull The previous example is a ldquoshallowrdquo clone
bull Fix the code to make a deep(er) cloneclass Node implements Cloneable Object data Node next public Object clone() Node nodeClone try nodeClone = (Node) superclone() catch( CloneNotSupportedException e) nodeClonesetData( thisdata )
nodeClonesetNext( )
CET230 -- Razdan et al 10
Really fix the shallow clonebull We still have a problem with the previous code
Nodes hold Object so clones are referencing the same data
bull What wersquod like to do is
bull But this has a problemndash We donrsquot know the actual class that ldquodatardquo belongs to ndash
it might not be Cloneable
bull To fix this check if ldquodatardquo is instanceof Cloneable If so we can do the ldquodeeprdquo clone If not then wersquore stuck with referencing the same ldquodatardquo object
nodeClonesetData(thisgetData()clone())
CET230 -- Razdan et al 11
List clone can use Node clonebull If a Node is Cloneable then the List clone
is pretty easy (all the work is done by the Node)
bull Consider the following (for List clone)
listClonehead = (Node) thisheadclone()
bull Now we just need to set listClonetail How about the followinglistClonetail = (Node) thistailclone()
bull What can we do
CET230 -- Razdan et al 12
Doubly Linked Listbull A doubly linked list allows us to store
references to the next node as well as the previous node
3 2 7 11
headtail
CET230 -- Razdan et al 13
Inheritance
bull A Doubly Linked List ldquois-ardquo List So we should take advantage of the List wersquove already implementedndash DoubleNode extends Nodendash DoubleList extends List
CET230 -- Razdan et al 14
Other Lists
bull Other types of lists are usefulndash Ordered list (elements in list are stored in some
order) Eg numbers are in increasing order strings are in alphabetical order etc
ndash Circular List the ldquoendrdquo of the list refers back to the head
ndash Skip Lists
CET230 -- Razdan et al 15
SkipList example from httpepaperpresscom
CET230 -- Razdan et al 16
Abstract Classesbull A robust implementation for List is to have an
ldquoAbstractListrdquo class from which concrete Lists (Singly Linked Doubly Linked Ordered etc) can be derived
bull An abstract classndash Has at least one abstract method (a method whose
interface is defined but NO implementation is specified by the class)
ndash Cannot be instantiatedndash Can provide implementation for some methodsndash Can provide attributes common to all concrete
subclasses
CET230 -- Razdan et al 17
Abstract List
bull Attributesndash head tail length
bull Methodsndash Constructor getLength equals clone
bull Abstract Methodsndash Add remove clone
CET230 -- Razdan et al 18
Implement clone in AbstractList
bull What Irsquod really like is to implement the clone() in the AbstractList classndash All Lists contain Nodes We donrsquot want to
rewrite the same code for the clone method over and over again in the concrete List classes
ndash Problem what about a DoubleList that contains DoubleNode The AbstractList implementation will not do enoughbecause the Node clone does not do enough
ndash But I WANT it to do enough
CET230 -- Razdan et al 19
Reflectionbull What if we made the Node clone ldquosmarterrdquo
ndash if itrsquos just a Node then do a Node clonendash if itrsquos some other kind of Node then do that
clonendash But the Node doesnrsquot know all the other classes
that extend it
bull Reflection can be used to obtain information about a class its members or its methods
CET230 -- Razdan et al 20
Reflection cont
bull The Class class (see javalang) has methods that enable us to get information about the classndash eg getMethod(String name Class
[] parameterTypes) returns ldquoMethodrdquo
bull The Method class (see javalangreflect) has methods that enable us to get information about the Method and even CALL the methodndash Object invoke(Object obj Object[] args)
CET230 -- Razdan et al 21
ldquoBionicrdquo Nodebull We can modify the Node clone as follows
Node nodeClonetry nodeClone = (Node) superclone() catch( CloneNotSupportedException e ) throw new CloneNotSupportedException()if( thisdata instanceof Cloneable ) try Class c = thisdatagetClass() Method m = cgetMethod( clone null )
nodeClonedata = minvoke( thisdata null ) catch( Exception e ) nodeClonedata = thisdata else nodeClonedata = thisdataif( thisnext = null ) nodeClonenext = (Node) thisnextclone()else nodeClonenext = nullreturn( nodeClone )
CET230 -- Razdan et al 22
Revisiting the String classbull Some useful String methods
ndash charAt( int index)
ndash indexOf( char ch )
ndash indexOf( String str )
ndash split( String regex )
ndash startsWith( String prefix )
ndash substring( int beginIndex int endIndex )
ndash toLowerCase()
ndash toUpperCase()
Note StringTokenizer is a legacy class that is retained for compatibility reasons although its use is discouraged in new code It is recommended that anyone seeking this functionality use the split method of String or the javautilregex package instead
CET230 -- Razdan et al 23
Using Files for IObull Using files for IO is similar to standard IObull For standard input you usually use
ndash InputStreamReaderndash BufferedReader
bull For standard output you usually usendash Systemoutprint or println
bull For file input you can usendash FileReaderndash BufferedReader
bull For file output you can usendash FileWriterndash BufferedWriter
CET230 -- Razdan et al 24
FileReader constructorFileReader
public FileReader(String fileName) throws FileNotFoundException
Creates a new FileReader given the name of the file to read from
Parameters fileName - the name of the file to read from
Throws FileNotFoundException - if the named file does not exist is a directory rather than a regular file or for some other reason cannot be opened for reading
CET230 -- Razdan et al 25
Read ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )
String s = inreadLine()int i = 1while( s = null )
Systemoutprintln(ldquoLine ldquo + i + ldquo ldquo + s )
i++s = inreadLine()
inclose()
CET230 -- Razdan et al 26
FileWriter constructor
FileWriter
public FileWriter(String fileName) throws IOException Constructs a FileWriter object given a file name
Parameters fileName - String The system-dependent filename
Throws IOException - if the named file exists but is a directory rather than a regular file does not exist but cannot be created or cannot be opened for any other reason
CET230 -- Razdan et al 27
BufferedWriter
Method Summary void
close() Close the stream
voidflush() Flush the stream
voidnewLine() Write a line separator
voidwrite(char[] cbuf int off int len) Write a portion of an array of characters
voidwrite(int c) Write a single character
voidwrite(String s int off int len) Write a portion of a String
CET230 -- Razdan et al 28
Write ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )BufferedWriter out = new BufferedWriter(
new FileWriter(outfile) )
String s = inreadLine()while( s = null )
outwrite((ssplit(ldquosrdquo))[0])outnewLine()s = inreadLine()
inclose()outclose()
CET230 -- Razdan et al 29
Java Interfaces
bull A Java interface is a set of related methods that a programmer may want to support in a single classndash Eg Cloneablendash Eg Comparablehttpjavasuncomj2se150docsapijavalangComparablehtml
CET230 -- Razdan et al 30
Iterator Pattern
bull Motivation ndash an aggregate object should give you a way to access its
elements without exposing its internal structure
ndash Use of the object may want to traverse the object in many different ways ndash donrsquot want to bloat the interface with may traversal methods even if you could anticipate all the methods needed
ndash May need to have more than one traversal pending on the aggregate at once
CET230 -- Razdan et al 31
Iterator Patternbull Key idea take responsibility for access and
traversal out of the object and put it into an iterator object
bull Iterator provides basic ldquonavigationrdquo methods eg ndash Firstndash Nextndash IsDonendash CurrentItem
CET230 -- Razdan et al 32
Map Interface
bull A map is a collection class in which keyvalue pairs may be added A pair can be retrieved or removed by specifying just its key
CET230 -- Razdan et al 33
TreeMap
bull Javarsquos TreeMapltK Vgt implements the map interface in an efficient way in which the keys are required to come from a class (such as String) that implements the Comparable interface
CET230 -- Razdan et al 34
Example
bull From package javautil
bull TreeMapltString Integergt frequencyData
bull String word
bull Integer count
CET230 -- Razdan et al 35
Operations
bull public V get(K key)
bull public V put(K key V value)
bull public boolean containsKey(K key)
bull public SetltKgt keySet()
bull public int size()
bull public void clear()
CET230 -- Razdan et al 36
Iteration
for (String word wordMapkeySet())
hellipprocess this key which is in variable wordhellip
CET230 -- Razdan et al 6
Wrapper Classes
bull A wrapper class is a class in which each object holds a primitive classndash Byte Short Integer Long Float Double
Character Boolean are wrapper classesndash Accessor methods xxxValue() where xxx is
primitive type
bull Note Java 15 provides ldquoauto-boxingrdquo which replaces need for Accessor methods
CET230 -- Razdan et al 7
Old vs Newbull Wrappers bull Boxing
ObjList L = new ObjList() must put primitive value 3 into an object (box it) in order to have an object to insert in the listLinsert( new Integer(3) )hellipInteger num = (Integer)LgetHead() now we must ldquoun-boxrdquo the primitive value int i = numintValue()
ObjList L = new ObjList() Java 15 will auto-boxLinsert( 3 )hellip Java 15 will auto-unboxint I = LgetHead()
bullSee httpjavasuncomj2se150docsguidelanguageautoboxinghtmlfor discussion on autoboxing
CET230 -- Razdan et al 8
Clones amp Deep Clonesbull Consider the following codeclass Node implements Cloneable private Object data private Node next
public Object clone() Node nodeClone try nodeClone = (Node) superclone() catch( CloneNotSupportedException e)
CET230 -- Razdan et al 9
Fix (kinda) previousbull The previous example is a ldquoshallowrdquo clone
bull Fix the code to make a deep(er) cloneclass Node implements Cloneable Object data Node next public Object clone() Node nodeClone try nodeClone = (Node) superclone() catch( CloneNotSupportedException e) nodeClonesetData( thisdata )
nodeClonesetNext( )
CET230 -- Razdan et al 10
Really fix the shallow clonebull We still have a problem with the previous code
Nodes hold Object so clones are referencing the same data
bull What wersquod like to do is
bull But this has a problemndash We donrsquot know the actual class that ldquodatardquo belongs to ndash
it might not be Cloneable
bull To fix this check if ldquodatardquo is instanceof Cloneable If so we can do the ldquodeeprdquo clone If not then wersquore stuck with referencing the same ldquodatardquo object
nodeClonesetData(thisgetData()clone())
CET230 -- Razdan et al 11
List clone can use Node clonebull If a Node is Cloneable then the List clone
is pretty easy (all the work is done by the Node)
bull Consider the following (for List clone)
listClonehead = (Node) thisheadclone()
bull Now we just need to set listClonetail How about the followinglistClonetail = (Node) thistailclone()
bull What can we do
CET230 -- Razdan et al 12
Doubly Linked Listbull A doubly linked list allows us to store
references to the next node as well as the previous node
3 2 7 11
headtail
CET230 -- Razdan et al 13
Inheritance
bull A Doubly Linked List ldquois-ardquo List So we should take advantage of the List wersquove already implementedndash DoubleNode extends Nodendash DoubleList extends List
CET230 -- Razdan et al 14
Other Lists
bull Other types of lists are usefulndash Ordered list (elements in list are stored in some
order) Eg numbers are in increasing order strings are in alphabetical order etc
ndash Circular List the ldquoendrdquo of the list refers back to the head
ndash Skip Lists
CET230 -- Razdan et al 15
SkipList example from httpepaperpresscom
CET230 -- Razdan et al 16
Abstract Classesbull A robust implementation for List is to have an
ldquoAbstractListrdquo class from which concrete Lists (Singly Linked Doubly Linked Ordered etc) can be derived
bull An abstract classndash Has at least one abstract method (a method whose
interface is defined but NO implementation is specified by the class)
ndash Cannot be instantiatedndash Can provide implementation for some methodsndash Can provide attributes common to all concrete
subclasses
CET230 -- Razdan et al 17
Abstract List
bull Attributesndash head tail length
bull Methodsndash Constructor getLength equals clone
bull Abstract Methodsndash Add remove clone
CET230 -- Razdan et al 18
Implement clone in AbstractList
bull What Irsquod really like is to implement the clone() in the AbstractList classndash All Lists contain Nodes We donrsquot want to
rewrite the same code for the clone method over and over again in the concrete List classes
ndash Problem what about a DoubleList that contains DoubleNode The AbstractList implementation will not do enoughbecause the Node clone does not do enough
ndash But I WANT it to do enough
CET230 -- Razdan et al 19
Reflectionbull What if we made the Node clone ldquosmarterrdquo
ndash if itrsquos just a Node then do a Node clonendash if itrsquos some other kind of Node then do that
clonendash But the Node doesnrsquot know all the other classes
that extend it
bull Reflection can be used to obtain information about a class its members or its methods
CET230 -- Razdan et al 20
Reflection cont
bull The Class class (see javalang) has methods that enable us to get information about the classndash eg getMethod(String name Class
[] parameterTypes) returns ldquoMethodrdquo
bull The Method class (see javalangreflect) has methods that enable us to get information about the Method and even CALL the methodndash Object invoke(Object obj Object[] args)
CET230 -- Razdan et al 21
ldquoBionicrdquo Nodebull We can modify the Node clone as follows
Node nodeClonetry nodeClone = (Node) superclone() catch( CloneNotSupportedException e ) throw new CloneNotSupportedException()if( thisdata instanceof Cloneable ) try Class c = thisdatagetClass() Method m = cgetMethod( clone null )
nodeClonedata = minvoke( thisdata null ) catch( Exception e ) nodeClonedata = thisdata else nodeClonedata = thisdataif( thisnext = null ) nodeClonenext = (Node) thisnextclone()else nodeClonenext = nullreturn( nodeClone )
CET230 -- Razdan et al 22
Revisiting the String classbull Some useful String methods
ndash charAt( int index)
ndash indexOf( char ch )
ndash indexOf( String str )
ndash split( String regex )
ndash startsWith( String prefix )
ndash substring( int beginIndex int endIndex )
ndash toLowerCase()
ndash toUpperCase()
Note StringTokenizer is a legacy class that is retained for compatibility reasons although its use is discouraged in new code It is recommended that anyone seeking this functionality use the split method of String or the javautilregex package instead
CET230 -- Razdan et al 23
Using Files for IObull Using files for IO is similar to standard IObull For standard input you usually use
ndash InputStreamReaderndash BufferedReader
bull For standard output you usually usendash Systemoutprint or println
bull For file input you can usendash FileReaderndash BufferedReader
bull For file output you can usendash FileWriterndash BufferedWriter
CET230 -- Razdan et al 24
FileReader constructorFileReader
public FileReader(String fileName) throws FileNotFoundException
Creates a new FileReader given the name of the file to read from
Parameters fileName - the name of the file to read from
Throws FileNotFoundException - if the named file does not exist is a directory rather than a regular file or for some other reason cannot be opened for reading
CET230 -- Razdan et al 25
Read ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )
String s = inreadLine()int i = 1while( s = null )
Systemoutprintln(ldquoLine ldquo + i + ldquo ldquo + s )
i++s = inreadLine()
inclose()
CET230 -- Razdan et al 26
FileWriter constructor
FileWriter
public FileWriter(String fileName) throws IOException Constructs a FileWriter object given a file name
Parameters fileName - String The system-dependent filename
Throws IOException - if the named file exists but is a directory rather than a regular file does not exist but cannot be created or cannot be opened for any other reason
CET230 -- Razdan et al 27
BufferedWriter
Method Summary void
close() Close the stream
voidflush() Flush the stream
voidnewLine() Write a line separator
voidwrite(char[] cbuf int off int len) Write a portion of an array of characters
voidwrite(int c) Write a single character
voidwrite(String s int off int len) Write a portion of a String
CET230 -- Razdan et al 28
Write ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )BufferedWriter out = new BufferedWriter(
new FileWriter(outfile) )
String s = inreadLine()while( s = null )
outwrite((ssplit(ldquosrdquo))[0])outnewLine()s = inreadLine()
inclose()outclose()
CET230 -- Razdan et al 29
Java Interfaces
bull A Java interface is a set of related methods that a programmer may want to support in a single classndash Eg Cloneablendash Eg Comparablehttpjavasuncomj2se150docsapijavalangComparablehtml
CET230 -- Razdan et al 30
Iterator Pattern
bull Motivation ndash an aggregate object should give you a way to access its
elements without exposing its internal structure
ndash Use of the object may want to traverse the object in many different ways ndash donrsquot want to bloat the interface with may traversal methods even if you could anticipate all the methods needed
ndash May need to have more than one traversal pending on the aggregate at once
CET230 -- Razdan et al 31
Iterator Patternbull Key idea take responsibility for access and
traversal out of the object and put it into an iterator object
bull Iterator provides basic ldquonavigationrdquo methods eg ndash Firstndash Nextndash IsDonendash CurrentItem
CET230 -- Razdan et al 32
Map Interface
bull A map is a collection class in which keyvalue pairs may be added A pair can be retrieved or removed by specifying just its key
CET230 -- Razdan et al 33
TreeMap
bull Javarsquos TreeMapltK Vgt implements the map interface in an efficient way in which the keys are required to come from a class (such as String) that implements the Comparable interface
CET230 -- Razdan et al 34
Example
bull From package javautil
bull TreeMapltString Integergt frequencyData
bull String word
bull Integer count
CET230 -- Razdan et al 35
Operations
bull public V get(K key)
bull public V put(K key V value)
bull public boolean containsKey(K key)
bull public SetltKgt keySet()
bull public int size()
bull public void clear()
CET230 -- Razdan et al 36
Iteration
for (String word wordMapkeySet())
hellipprocess this key which is in variable wordhellip
CET230 -- Razdan et al 7
Old vs Newbull Wrappers bull Boxing
ObjList L = new ObjList() must put primitive value 3 into an object (box it) in order to have an object to insert in the listLinsert( new Integer(3) )hellipInteger num = (Integer)LgetHead() now we must ldquoun-boxrdquo the primitive value int i = numintValue()
ObjList L = new ObjList() Java 15 will auto-boxLinsert( 3 )hellip Java 15 will auto-unboxint I = LgetHead()
bullSee httpjavasuncomj2se150docsguidelanguageautoboxinghtmlfor discussion on autoboxing
CET230 -- Razdan et al 8
Clones amp Deep Clonesbull Consider the following codeclass Node implements Cloneable private Object data private Node next
public Object clone() Node nodeClone try nodeClone = (Node) superclone() catch( CloneNotSupportedException e)
CET230 -- Razdan et al 9
Fix (kinda) previousbull The previous example is a ldquoshallowrdquo clone
bull Fix the code to make a deep(er) cloneclass Node implements Cloneable Object data Node next public Object clone() Node nodeClone try nodeClone = (Node) superclone() catch( CloneNotSupportedException e) nodeClonesetData( thisdata )
nodeClonesetNext( )
CET230 -- Razdan et al 10
Really fix the shallow clonebull We still have a problem with the previous code
Nodes hold Object so clones are referencing the same data
bull What wersquod like to do is
bull But this has a problemndash We donrsquot know the actual class that ldquodatardquo belongs to ndash
it might not be Cloneable
bull To fix this check if ldquodatardquo is instanceof Cloneable If so we can do the ldquodeeprdquo clone If not then wersquore stuck with referencing the same ldquodatardquo object
nodeClonesetData(thisgetData()clone())
CET230 -- Razdan et al 11
List clone can use Node clonebull If a Node is Cloneable then the List clone
is pretty easy (all the work is done by the Node)
bull Consider the following (for List clone)
listClonehead = (Node) thisheadclone()
bull Now we just need to set listClonetail How about the followinglistClonetail = (Node) thistailclone()
bull What can we do
CET230 -- Razdan et al 12
Doubly Linked Listbull A doubly linked list allows us to store
references to the next node as well as the previous node
3 2 7 11
headtail
CET230 -- Razdan et al 13
Inheritance
bull A Doubly Linked List ldquois-ardquo List So we should take advantage of the List wersquove already implementedndash DoubleNode extends Nodendash DoubleList extends List
CET230 -- Razdan et al 14
Other Lists
bull Other types of lists are usefulndash Ordered list (elements in list are stored in some
order) Eg numbers are in increasing order strings are in alphabetical order etc
ndash Circular List the ldquoendrdquo of the list refers back to the head
ndash Skip Lists
CET230 -- Razdan et al 15
SkipList example from httpepaperpresscom
CET230 -- Razdan et al 16
Abstract Classesbull A robust implementation for List is to have an
ldquoAbstractListrdquo class from which concrete Lists (Singly Linked Doubly Linked Ordered etc) can be derived
bull An abstract classndash Has at least one abstract method (a method whose
interface is defined but NO implementation is specified by the class)
ndash Cannot be instantiatedndash Can provide implementation for some methodsndash Can provide attributes common to all concrete
subclasses
CET230 -- Razdan et al 17
Abstract List
bull Attributesndash head tail length
bull Methodsndash Constructor getLength equals clone
bull Abstract Methodsndash Add remove clone
CET230 -- Razdan et al 18
Implement clone in AbstractList
bull What Irsquod really like is to implement the clone() in the AbstractList classndash All Lists contain Nodes We donrsquot want to
rewrite the same code for the clone method over and over again in the concrete List classes
ndash Problem what about a DoubleList that contains DoubleNode The AbstractList implementation will not do enoughbecause the Node clone does not do enough
ndash But I WANT it to do enough
CET230 -- Razdan et al 19
Reflectionbull What if we made the Node clone ldquosmarterrdquo
ndash if itrsquos just a Node then do a Node clonendash if itrsquos some other kind of Node then do that
clonendash But the Node doesnrsquot know all the other classes
that extend it
bull Reflection can be used to obtain information about a class its members or its methods
CET230 -- Razdan et al 20
Reflection cont
bull The Class class (see javalang) has methods that enable us to get information about the classndash eg getMethod(String name Class
[] parameterTypes) returns ldquoMethodrdquo
bull The Method class (see javalangreflect) has methods that enable us to get information about the Method and even CALL the methodndash Object invoke(Object obj Object[] args)
CET230 -- Razdan et al 21
ldquoBionicrdquo Nodebull We can modify the Node clone as follows
Node nodeClonetry nodeClone = (Node) superclone() catch( CloneNotSupportedException e ) throw new CloneNotSupportedException()if( thisdata instanceof Cloneable ) try Class c = thisdatagetClass() Method m = cgetMethod( clone null )
nodeClonedata = minvoke( thisdata null ) catch( Exception e ) nodeClonedata = thisdata else nodeClonedata = thisdataif( thisnext = null ) nodeClonenext = (Node) thisnextclone()else nodeClonenext = nullreturn( nodeClone )
CET230 -- Razdan et al 22
Revisiting the String classbull Some useful String methods
ndash charAt( int index)
ndash indexOf( char ch )
ndash indexOf( String str )
ndash split( String regex )
ndash startsWith( String prefix )
ndash substring( int beginIndex int endIndex )
ndash toLowerCase()
ndash toUpperCase()
Note StringTokenizer is a legacy class that is retained for compatibility reasons although its use is discouraged in new code It is recommended that anyone seeking this functionality use the split method of String or the javautilregex package instead
CET230 -- Razdan et al 23
Using Files for IObull Using files for IO is similar to standard IObull For standard input you usually use
ndash InputStreamReaderndash BufferedReader
bull For standard output you usually usendash Systemoutprint or println
bull For file input you can usendash FileReaderndash BufferedReader
bull For file output you can usendash FileWriterndash BufferedWriter
CET230 -- Razdan et al 24
FileReader constructorFileReader
public FileReader(String fileName) throws FileNotFoundException
Creates a new FileReader given the name of the file to read from
Parameters fileName - the name of the file to read from
Throws FileNotFoundException - if the named file does not exist is a directory rather than a regular file or for some other reason cannot be opened for reading
CET230 -- Razdan et al 25
Read ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )
String s = inreadLine()int i = 1while( s = null )
Systemoutprintln(ldquoLine ldquo + i + ldquo ldquo + s )
i++s = inreadLine()
inclose()
CET230 -- Razdan et al 26
FileWriter constructor
FileWriter
public FileWriter(String fileName) throws IOException Constructs a FileWriter object given a file name
Parameters fileName - String The system-dependent filename
Throws IOException - if the named file exists but is a directory rather than a regular file does not exist but cannot be created or cannot be opened for any other reason
CET230 -- Razdan et al 27
BufferedWriter
Method Summary void
close() Close the stream
voidflush() Flush the stream
voidnewLine() Write a line separator
voidwrite(char[] cbuf int off int len) Write a portion of an array of characters
voidwrite(int c) Write a single character
voidwrite(String s int off int len) Write a portion of a String
CET230 -- Razdan et al 28
Write ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )BufferedWriter out = new BufferedWriter(
new FileWriter(outfile) )
String s = inreadLine()while( s = null )
outwrite((ssplit(ldquosrdquo))[0])outnewLine()s = inreadLine()
inclose()outclose()
CET230 -- Razdan et al 29
Java Interfaces
bull A Java interface is a set of related methods that a programmer may want to support in a single classndash Eg Cloneablendash Eg Comparablehttpjavasuncomj2se150docsapijavalangComparablehtml
CET230 -- Razdan et al 30
Iterator Pattern
bull Motivation ndash an aggregate object should give you a way to access its
elements without exposing its internal structure
ndash Use of the object may want to traverse the object in many different ways ndash donrsquot want to bloat the interface with may traversal methods even if you could anticipate all the methods needed
ndash May need to have more than one traversal pending on the aggregate at once
CET230 -- Razdan et al 31
Iterator Patternbull Key idea take responsibility for access and
traversal out of the object and put it into an iterator object
bull Iterator provides basic ldquonavigationrdquo methods eg ndash Firstndash Nextndash IsDonendash CurrentItem
CET230 -- Razdan et al 32
Map Interface
bull A map is a collection class in which keyvalue pairs may be added A pair can be retrieved or removed by specifying just its key
CET230 -- Razdan et al 33
TreeMap
bull Javarsquos TreeMapltK Vgt implements the map interface in an efficient way in which the keys are required to come from a class (such as String) that implements the Comparable interface
CET230 -- Razdan et al 34
Example
bull From package javautil
bull TreeMapltString Integergt frequencyData
bull String word
bull Integer count
CET230 -- Razdan et al 35
Operations
bull public V get(K key)
bull public V put(K key V value)
bull public boolean containsKey(K key)
bull public SetltKgt keySet()
bull public int size()
bull public void clear()
CET230 -- Razdan et al 36
Iteration
for (String word wordMapkeySet())
hellipprocess this key which is in variable wordhellip
CET230 -- Razdan et al 8
Clones amp Deep Clonesbull Consider the following codeclass Node implements Cloneable private Object data private Node next
public Object clone() Node nodeClone try nodeClone = (Node) superclone() catch( CloneNotSupportedException e)
CET230 -- Razdan et al 9
Fix (kinda) previousbull The previous example is a ldquoshallowrdquo clone
bull Fix the code to make a deep(er) cloneclass Node implements Cloneable Object data Node next public Object clone() Node nodeClone try nodeClone = (Node) superclone() catch( CloneNotSupportedException e) nodeClonesetData( thisdata )
nodeClonesetNext( )
CET230 -- Razdan et al 10
Really fix the shallow clonebull We still have a problem with the previous code
Nodes hold Object so clones are referencing the same data
bull What wersquod like to do is
bull But this has a problemndash We donrsquot know the actual class that ldquodatardquo belongs to ndash
it might not be Cloneable
bull To fix this check if ldquodatardquo is instanceof Cloneable If so we can do the ldquodeeprdquo clone If not then wersquore stuck with referencing the same ldquodatardquo object
nodeClonesetData(thisgetData()clone())
CET230 -- Razdan et al 11
List clone can use Node clonebull If a Node is Cloneable then the List clone
is pretty easy (all the work is done by the Node)
bull Consider the following (for List clone)
listClonehead = (Node) thisheadclone()
bull Now we just need to set listClonetail How about the followinglistClonetail = (Node) thistailclone()
bull What can we do
CET230 -- Razdan et al 12
Doubly Linked Listbull A doubly linked list allows us to store
references to the next node as well as the previous node
3 2 7 11
headtail
CET230 -- Razdan et al 13
Inheritance
bull A Doubly Linked List ldquois-ardquo List So we should take advantage of the List wersquove already implementedndash DoubleNode extends Nodendash DoubleList extends List
CET230 -- Razdan et al 14
Other Lists
bull Other types of lists are usefulndash Ordered list (elements in list are stored in some
order) Eg numbers are in increasing order strings are in alphabetical order etc
ndash Circular List the ldquoendrdquo of the list refers back to the head
ndash Skip Lists
CET230 -- Razdan et al 15
SkipList example from httpepaperpresscom
CET230 -- Razdan et al 16
Abstract Classesbull A robust implementation for List is to have an
ldquoAbstractListrdquo class from which concrete Lists (Singly Linked Doubly Linked Ordered etc) can be derived
bull An abstract classndash Has at least one abstract method (a method whose
interface is defined but NO implementation is specified by the class)
ndash Cannot be instantiatedndash Can provide implementation for some methodsndash Can provide attributes common to all concrete
subclasses
CET230 -- Razdan et al 17
Abstract List
bull Attributesndash head tail length
bull Methodsndash Constructor getLength equals clone
bull Abstract Methodsndash Add remove clone
CET230 -- Razdan et al 18
Implement clone in AbstractList
bull What Irsquod really like is to implement the clone() in the AbstractList classndash All Lists contain Nodes We donrsquot want to
rewrite the same code for the clone method over and over again in the concrete List classes
ndash Problem what about a DoubleList that contains DoubleNode The AbstractList implementation will not do enoughbecause the Node clone does not do enough
ndash But I WANT it to do enough
CET230 -- Razdan et al 19
Reflectionbull What if we made the Node clone ldquosmarterrdquo
ndash if itrsquos just a Node then do a Node clonendash if itrsquos some other kind of Node then do that
clonendash But the Node doesnrsquot know all the other classes
that extend it
bull Reflection can be used to obtain information about a class its members or its methods
CET230 -- Razdan et al 20
Reflection cont
bull The Class class (see javalang) has methods that enable us to get information about the classndash eg getMethod(String name Class
[] parameterTypes) returns ldquoMethodrdquo
bull The Method class (see javalangreflect) has methods that enable us to get information about the Method and even CALL the methodndash Object invoke(Object obj Object[] args)
CET230 -- Razdan et al 21
ldquoBionicrdquo Nodebull We can modify the Node clone as follows
Node nodeClonetry nodeClone = (Node) superclone() catch( CloneNotSupportedException e ) throw new CloneNotSupportedException()if( thisdata instanceof Cloneable ) try Class c = thisdatagetClass() Method m = cgetMethod( clone null )
nodeClonedata = minvoke( thisdata null ) catch( Exception e ) nodeClonedata = thisdata else nodeClonedata = thisdataif( thisnext = null ) nodeClonenext = (Node) thisnextclone()else nodeClonenext = nullreturn( nodeClone )
CET230 -- Razdan et al 22
Revisiting the String classbull Some useful String methods
ndash charAt( int index)
ndash indexOf( char ch )
ndash indexOf( String str )
ndash split( String regex )
ndash startsWith( String prefix )
ndash substring( int beginIndex int endIndex )
ndash toLowerCase()
ndash toUpperCase()
Note StringTokenizer is a legacy class that is retained for compatibility reasons although its use is discouraged in new code It is recommended that anyone seeking this functionality use the split method of String or the javautilregex package instead
CET230 -- Razdan et al 23
Using Files for IObull Using files for IO is similar to standard IObull For standard input you usually use
ndash InputStreamReaderndash BufferedReader
bull For standard output you usually usendash Systemoutprint or println
bull For file input you can usendash FileReaderndash BufferedReader
bull For file output you can usendash FileWriterndash BufferedWriter
CET230 -- Razdan et al 24
FileReader constructorFileReader
public FileReader(String fileName) throws FileNotFoundException
Creates a new FileReader given the name of the file to read from
Parameters fileName - the name of the file to read from
Throws FileNotFoundException - if the named file does not exist is a directory rather than a regular file or for some other reason cannot be opened for reading
CET230 -- Razdan et al 25
Read ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )
String s = inreadLine()int i = 1while( s = null )
Systemoutprintln(ldquoLine ldquo + i + ldquo ldquo + s )
i++s = inreadLine()
inclose()
CET230 -- Razdan et al 26
FileWriter constructor
FileWriter
public FileWriter(String fileName) throws IOException Constructs a FileWriter object given a file name
Parameters fileName - String The system-dependent filename
Throws IOException - if the named file exists but is a directory rather than a regular file does not exist but cannot be created or cannot be opened for any other reason
CET230 -- Razdan et al 27
BufferedWriter
Method Summary void
close() Close the stream
voidflush() Flush the stream
voidnewLine() Write a line separator
voidwrite(char[] cbuf int off int len) Write a portion of an array of characters
voidwrite(int c) Write a single character
voidwrite(String s int off int len) Write a portion of a String
CET230 -- Razdan et al 28
Write ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )BufferedWriter out = new BufferedWriter(
new FileWriter(outfile) )
String s = inreadLine()while( s = null )
outwrite((ssplit(ldquosrdquo))[0])outnewLine()s = inreadLine()
inclose()outclose()
CET230 -- Razdan et al 29
Java Interfaces
bull A Java interface is a set of related methods that a programmer may want to support in a single classndash Eg Cloneablendash Eg Comparablehttpjavasuncomj2se150docsapijavalangComparablehtml
CET230 -- Razdan et al 30
Iterator Pattern
bull Motivation ndash an aggregate object should give you a way to access its
elements without exposing its internal structure
ndash Use of the object may want to traverse the object in many different ways ndash donrsquot want to bloat the interface with may traversal methods even if you could anticipate all the methods needed
ndash May need to have more than one traversal pending on the aggregate at once
CET230 -- Razdan et al 31
Iterator Patternbull Key idea take responsibility for access and
traversal out of the object and put it into an iterator object
bull Iterator provides basic ldquonavigationrdquo methods eg ndash Firstndash Nextndash IsDonendash CurrentItem
CET230 -- Razdan et al 32
Map Interface
bull A map is a collection class in which keyvalue pairs may be added A pair can be retrieved or removed by specifying just its key
CET230 -- Razdan et al 33
TreeMap
bull Javarsquos TreeMapltK Vgt implements the map interface in an efficient way in which the keys are required to come from a class (such as String) that implements the Comparable interface
CET230 -- Razdan et al 34
Example
bull From package javautil
bull TreeMapltString Integergt frequencyData
bull String word
bull Integer count
CET230 -- Razdan et al 35
Operations
bull public V get(K key)
bull public V put(K key V value)
bull public boolean containsKey(K key)
bull public SetltKgt keySet()
bull public int size()
bull public void clear()
CET230 -- Razdan et al 36
Iteration
for (String word wordMapkeySet())
hellipprocess this key which is in variable wordhellip
CET230 -- Razdan et al 9
Fix (kinda) previousbull The previous example is a ldquoshallowrdquo clone
bull Fix the code to make a deep(er) cloneclass Node implements Cloneable Object data Node next public Object clone() Node nodeClone try nodeClone = (Node) superclone() catch( CloneNotSupportedException e) nodeClonesetData( thisdata )
nodeClonesetNext( )
CET230 -- Razdan et al 10
Really fix the shallow clonebull We still have a problem with the previous code
Nodes hold Object so clones are referencing the same data
bull What wersquod like to do is
bull But this has a problemndash We donrsquot know the actual class that ldquodatardquo belongs to ndash
it might not be Cloneable
bull To fix this check if ldquodatardquo is instanceof Cloneable If so we can do the ldquodeeprdquo clone If not then wersquore stuck with referencing the same ldquodatardquo object
nodeClonesetData(thisgetData()clone())
CET230 -- Razdan et al 11
List clone can use Node clonebull If a Node is Cloneable then the List clone
is pretty easy (all the work is done by the Node)
bull Consider the following (for List clone)
listClonehead = (Node) thisheadclone()
bull Now we just need to set listClonetail How about the followinglistClonetail = (Node) thistailclone()
bull What can we do
CET230 -- Razdan et al 12
Doubly Linked Listbull A doubly linked list allows us to store
references to the next node as well as the previous node
3 2 7 11
headtail
CET230 -- Razdan et al 13
Inheritance
bull A Doubly Linked List ldquois-ardquo List So we should take advantage of the List wersquove already implementedndash DoubleNode extends Nodendash DoubleList extends List
CET230 -- Razdan et al 14
Other Lists
bull Other types of lists are usefulndash Ordered list (elements in list are stored in some
order) Eg numbers are in increasing order strings are in alphabetical order etc
ndash Circular List the ldquoendrdquo of the list refers back to the head
ndash Skip Lists
CET230 -- Razdan et al 15
SkipList example from httpepaperpresscom
CET230 -- Razdan et al 16
Abstract Classesbull A robust implementation for List is to have an
ldquoAbstractListrdquo class from which concrete Lists (Singly Linked Doubly Linked Ordered etc) can be derived
bull An abstract classndash Has at least one abstract method (a method whose
interface is defined but NO implementation is specified by the class)
ndash Cannot be instantiatedndash Can provide implementation for some methodsndash Can provide attributes common to all concrete
subclasses
CET230 -- Razdan et al 17
Abstract List
bull Attributesndash head tail length
bull Methodsndash Constructor getLength equals clone
bull Abstract Methodsndash Add remove clone
CET230 -- Razdan et al 18
Implement clone in AbstractList
bull What Irsquod really like is to implement the clone() in the AbstractList classndash All Lists contain Nodes We donrsquot want to
rewrite the same code for the clone method over and over again in the concrete List classes
ndash Problem what about a DoubleList that contains DoubleNode The AbstractList implementation will not do enoughbecause the Node clone does not do enough
ndash But I WANT it to do enough
CET230 -- Razdan et al 19
Reflectionbull What if we made the Node clone ldquosmarterrdquo
ndash if itrsquos just a Node then do a Node clonendash if itrsquos some other kind of Node then do that
clonendash But the Node doesnrsquot know all the other classes
that extend it
bull Reflection can be used to obtain information about a class its members or its methods
CET230 -- Razdan et al 20
Reflection cont
bull The Class class (see javalang) has methods that enable us to get information about the classndash eg getMethod(String name Class
[] parameterTypes) returns ldquoMethodrdquo
bull The Method class (see javalangreflect) has methods that enable us to get information about the Method and even CALL the methodndash Object invoke(Object obj Object[] args)
CET230 -- Razdan et al 21
ldquoBionicrdquo Nodebull We can modify the Node clone as follows
Node nodeClonetry nodeClone = (Node) superclone() catch( CloneNotSupportedException e ) throw new CloneNotSupportedException()if( thisdata instanceof Cloneable ) try Class c = thisdatagetClass() Method m = cgetMethod( clone null )
nodeClonedata = minvoke( thisdata null ) catch( Exception e ) nodeClonedata = thisdata else nodeClonedata = thisdataif( thisnext = null ) nodeClonenext = (Node) thisnextclone()else nodeClonenext = nullreturn( nodeClone )
CET230 -- Razdan et al 22
Revisiting the String classbull Some useful String methods
ndash charAt( int index)
ndash indexOf( char ch )
ndash indexOf( String str )
ndash split( String regex )
ndash startsWith( String prefix )
ndash substring( int beginIndex int endIndex )
ndash toLowerCase()
ndash toUpperCase()
Note StringTokenizer is a legacy class that is retained for compatibility reasons although its use is discouraged in new code It is recommended that anyone seeking this functionality use the split method of String or the javautilregex package instead
CET230 -- Razdan et al 23
Using Files for IObull Using files for IO is similar to standard IObull For standard input you usually use
ndash InputStreamReaderndash BufferedReader
bull For standard output you usually usendash Systemoutprint or println
bull For file input you can usendash FileReaderndash BufferedReader
bull For file output you can usendash FileWriterndash BufferedWriter
CET230 -- Razdan et al 24
FileReader constructorFileReader
public FileReader(String fileName) throws FileNotFoundException
Creates a new FileReader given the name of the file to read from
Parameters fileName - the name of the file to read from
Throws FileNotFoundException - if the named file does not exist is a directory rather than a regular file or for some other reason cannot be opened for reading
CET230 -- Razdan et al 25
Read ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )
String s = inreadLine()int i = 1while( s = null )
Systemoutprintln(ldquoLine ldquo + i + ldquo ldquo + s )
i++s = inreadLine()
inclose()
CET230 -- Razdan et al 26
FileWriter constructor
FileWriter
public FileWriter(String fileName) throws IOException Constructs a FileWriter object given a file name
Parameters fileName - String The system-dependent filename
Throws IOException - if the named file exists but is a directory rather than a regular file does not exist but cannot be created or cannot be opened for any other reason
CET230 -- Razdan et al 27
BufferedWriter
Method Summary void
close() Close the stream
voidflush() Flush the stream
voidnewLine() Write a line separator
voidwrite(char[] cbuf int off int len) Write a portion of an array of characters
voidwrite(int c) Write a single character
voidwrite(String s int off int len) Write a portion of a String
CET230 -- Razdan et al 28
Write ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )BufferedWriter out = new BufferedWriter(
new FileWriter(outfile) )
String s = inreadLine()while( s = null )
outwrite((ssplit(ldquosrdquo))[0])outnewLine()s = inreadLine()
inclose()outclose()
CET230 -- Razdan et al 29
Java Interfaces
bull A Java interface is a set of related methods that a programmer may want to support in a single classndash Eg Cloneablendash Eg Comparablehttpjavasuncomj2se150docsapijavalangComparablehtml
CET230 -- Razdan et al 30
Iterator Pattern
bull Motivation ndash an aggregate object should give you a way to access its
elements without exposing its internal structure
ndash Use of the object may want to traverse the object in many different ways ndash donrsquot want to bloat the interface with may traversal methods even if you could anticipate all the methods needed
ndash May need to have more than one traversal pending on the aggregate at once
CET230 -- Razdan et al 31
Iterator Patternbull Key idea take responsibility for access and
traversal out of the object and put it into an iterator object
bull Iterator provides basic ldquonavigationrdquo methods eg ndash Firstndash Nextndash IsDonendash CurrentItem
CET230 -- Razdan et al 32
Map Interface
bull A map is a collection class in which keyvalue pairs may be added A pair can be retrieved or removed by specifying just its key
CET230 -- Razdan et al 33
TreeMap
bull Javarsquos TreeMapltK Vgt implements the map interface in an efficient way in which the keys are required to come from a class (such as String) that implements the Comparable interface
CET230 -- Razdan et al 34
Example
bull From package javautil
bull TreeMapltString Integergt frequencyData
bull String word
bull Integer count
CET230 -- Razdan et al 35
Operations
bull public V get(K key)
bull public V put(K key V value)
bull public boolean containsKey(K key)
bull public SetltKgt keySet()
bull public int size()
bull public void clear()
CET230 -- Razdan et al 36
Iteration
for (String word wordMapkeySet())
hellipprocess this key which is in variable wordhellip
CET230 -- Razdan et al 10
Really fix the shallow clonebull We still have a problem with the previous code
Nodes hold Object so clones are referencing the same data
bull What wersquod like to do is
bull But this has a problemndash We donrsquot know the actual class that ldquodatardquo belongs to ndash
it might not be Cloneable
bull To fix this check if ldquodatardquo is instanceof Cloneable If so we can do the ldquodeeprdquo clone If not then wersquore stuck with referencing the same ldquodatardquo object
nodeClonesetData(thisgetData()clone())
CET230 -- Razdan et al 11
List clone can use Node clonebull If a Node is Cloneable then the List clone
is pretty easy (all the work is done by the Node)
bull Consider the following (for List clone)
listClonehead = (Node) thisheadclone()
bull Now we just need to set listClonetail How about the followinglistClonetail = (Node) thistailclone()
bull What can we do
CET230 -- Razdan et al 12
Doubly Linked Listbull A doubly linked list allows us to store
references to the next node as well as the previous node
3 2 7 11
headtail
CET230 -- Razdan et al 13
Inheritance
bull A Doubly Linked List ldquois-ardquo List So we should take advantage of the List wersquove already implementedndash DoubleNode extends Nodendash DoubleList extends List
CET230 -- Razdan et al 14
Other Lists
bull Other types of lists are usefulndash Ordered list (elements in list are stored in some
order) Eg numbers are in increasing order strings are in alphabetical order etc
ndash Circular List the ldquoendrdquo of the list refers back to the head
ndash Skip Lists
CET230 -- Razdan et al 15
SkipList example from httpepaperpresscom
CET230 -- Razdan et al 16
Abstract Classesbull A robust implementation for List is to have an
ldquoAbstractListrdquo class from which concrete Lists (Singly Linked Doubly Linked Ordered etc) can be derived
bull An abstract classndash Has at least one abstract method (a method whose
interface is defined but NO implementation is specified by the class)
ndash Cannot be instantiatedndash Can provide implementation for some methodsndash Can provide attributes common to all concrete
subclasses
CET230 -- Razdan et al 17
Abstract List
bull Attributesndash head tail length
bull Methodsndash Constructor getLength equals clone
bull Abstract Methodsndash Add remove clone
CET230 -- Razdan et al 18
Implement clone in AbstractList
bull What Irsquod really like is to implement the clone() in the AbstractList classndash All Lists contain Nodes We donrsquot want to
rewrite the same code for the clone method over and over again in the concrete List classes
ndash Problem what about a DoubleList that contains DoubleNode The AbstractList implementation will not do enoughbecause the Node clone does not do enough
ndash But I WANT it to do enough
CET230 -- Razdan et al 19
Reflectionbull What if we made the Node clone ldquosmarterrdquo
ndash if itrsquos just a Node then do a Node clonendash if itrsquos some other kind of Node then do that
clonendash But the Node doesnrsquot know all the other classes
that extend it
bull Reflection can be used to obtain information about a class its members or its methods
CET230 -- Razdan et al 20
Reflection cont
bull The Class class (see javalang) has methods that enable us to get information about the classndash eg getMethod(String name Class
[] parameterTypes) returns ldquoMethodrdquo
bull The Method class (see javalangreflect) has methods that enable us to get information about the Method and even CALL the methodndash Object invoke(Object obj Object[] args)
CET230 -- Razdan et al 21
ldquoBionicrdquo Nodebull We can modify the Node clone as follows
Node nodeClonetry nodeClone = (Node) superclone() catch( CloneNotSupportedException e ) throw new CloneNotSupportedException()if( thisdata instanceof Cloneable ) try Class c = thisdatagetClass() Method m = cgetMethod( clone null )
nodeClonedata = minvoke( thisdata null ) catch( Exception e ) nodeClonedata = thisdata else nodeClonedata = thisdataif( thisnext = null ) nodeClonenext = (Node) thisnextclone()else nodeClonenext = nullreturn( nodeClone )
CET230 -- Razdan et al 22
Revisiting the String classbull Some useful String methods
ndash charAt( int index)
ndash indexOf( char ch )
ndash indexOf( String str )
ndash split( String regex )
ndash startsWith( String prefix )
ndash substring( int beginIndex int endIndex )
ndash toLowerCase()
ndash toUpperCase()
Note StringTokenizer is a legacy class that is retained for compatibility reasons although its use is discouraged in new code It is recommended that anyone seeking this functionality use the split method of String or the javautilregex package instead
CET230 -- Razdan et al 23
Using Files for IObull Using files for IO is similar to standard IObull For standard input you usually use
ndash InputStreamReaderndash BufferedReader
bull For standard output you usually usendash Systemoutprint or println
bull For file input you can usendash FileReaderndash BufferedReader
bull For file output you can usendash FileWriterndash BufferedWriter
CET230 -- Razdan et al 24
FileReader constructorFileReader
public FileReader(String fileName) throws FileNotFoundException
Creates a new FileReader given the name of the file to read from
Parameters fileName - the name of the file to read from
Throws FileNotFoundException - if the named file does not exist is a directory rather than a regular file or for some other reason cannot be opened for reading
CET230 -- Razdan et al 25
Read ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )
String s = inreadLine()int i = 1while( s = null )
Systemoutprintln(ldquoLine ldquo + i + ldquo ldquo + s )
i++s = inreadLine()
inclose()
CET230 -- Razdan et al 26
FileWriter constructor
FileWriter
public FileWriter(String fileName) throws IOException Constructs a FileWriter object given a file name
Parameters fileName - String The system-dependent filename
Throws IOException - if the named file exists but is a directory rather than a regular file does not exist but cannot be created or cannot be opened for any other reason
CET230 -- Razdan et al 27
BufferedWriter
Method Summary void
close() Close the stream
voidflush() Flush the stream
voidnewLine() Write a line separator
voidwrite(char[] cbuf int off int len) Write a portion of an array of characters
voidwrite(int c) Write a single character
voidwrite(String s int off int len) Write a portion of a String
CET230 -- Razdan et al 28
Write ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )BufferedWriter out = new BufferedWriter(
new FileWriter(outfile) )
String s = inreadLine()while( s = null )
outwrite((ssplit(ldquosrdquo))[0])outnewLine()s = inreadLine()
inclose()outclose()
CET230 -- Razdan et al 29
Java Interfaces
bull A Java interface is a set of related methods that a programmer may want to support in a single classndash Eg Cloneablendash Eg Comparablehttpjavasuncomj2se150docsapijavalangComparablehtml
CET230 -- Razdan et al 30
Iterator Pattern
bull Motivation ndash an aggregate object should give you a way to access its
elements without exposing its internal structure
ndash Use of the object may want to traverse the object in many different ways ndash donrsquot want to bloat the interface with may traversal methods even if you could anticipate all the methods needed
ndash May need to have more than one traversal pending on the aggregate at once
CET230 -- Razdan et al 31
Iterator Patternbull Key idea take responsibility for access and
traversal out of the object and put it into an iterator object
bull Iterator provides basic ldquonavigationrdquo methods eg ndash Firstndash Nextndash IsDonendash CurrentItem
CET230 -- Razdan et al 32
Map Interface
bull A map is a collection class in which keyvalue pairs may be added A pair can be retrieved or removed by specifying just its key
CET230 -- Razdan et al 33
TreeMap
bull Javarsquos TreeMapltK Vgt implements the map interface in an efficient way in which the keys are required to come from a class (such as String) that implements the Comparable interface
CET230 -- Razdan et al 34
Example
bull From package javautil
bull TreeMapltString Integergt frequencyData
bull String word
bull Integer count
CET230 -- Razdan et al 35
Operations
bull public V get(K key)
bull public V put(K key V value)
bull public boolean containsKey(K key)
bull public SetltKgt keySet()
bull public int size()
bull public void clear()
CET230 -- Razdan et al 36
Iteration
for (String word wordMapkeySet())
hellipprocess this key which is in variable wordhellip
CET230 -- Razdan et al 11
List clone can use Node clonebull If a Node is Cloneable then the List clone
is pretty easy (all the work is done by the Node)
bull Consider the following (for List clone)
listClonehead = (Node) thisheadclone()
bull Now we just need to set listClonetail How about the followinglistClonetail = (Node) thistailclone()
bull What can we do
CET230 -- Razdan et al 12
Doubly Linked Listbull A doubly linked list allows us to store
references to the next node as well as the previous node
3 2 7 11
headtail
CET230 -- Razdan et al 13
Inheritance
bull A Doubly Linked List ldquois-ardquo List So we should take advantage of the List wersquove already implementedndash DoubleNode extends Nodendash DoubleList extends List
CET230 -- Razdan et al 14
Other Lists
bull Other types of lists are usefulndash Ordered list (elements in list are stored in some
order) Eg numbers are in increasing order strings are in alphabetical order etc
ndash Circular List the ldquoendrdquo of the list refers back to the head
ndash Skip Lists
CET230 -- Razdan et al 15
SkipList example from httpepaperpresscom
CET230 -- Razdan et al 16
Abstract Classesbull A robust implementation for List is to have an
ldquoAbstractListrdquo class from which concrete Lists (Singly Linked Doubly Linked Ordered etc) can be derived
bull An abstract classndash Has at least one abstract method (a method whose
interface is defined but NO implementation is specified by the class)
ndash Cannot be instantiatedndash Can provide implementation for some methodsndash Can provide attributes common to all concrete
subclasses
CET230 -- Razdan et al 17
Abstract List
bull Attributesndash head tail length
bull Methodsndash Constructor getLength equals clone
bull Abstract Methodsndash Add remove clone
CET230 -- Razdan et al 18
Implement clone in AbstractList
bull What Irsquod really like is to implement the clone() in the AbstractList classndash All Lists contain Nodes We donrsquot want to
rewrite the same code for the clone method over and over again in the concrete List classes
ndash Problem what about a DoubleList that contains DoubleNode The AbstractList implementation will not do enoughbecause the Node clone does not do enough
ndash But I WANT it to do enough
CET230 -- Razdan et al 19
Reflectionbull What if we made the Node clone ldquosmarterrdquo
ndash if itrsquos just a Node then do a Node clonendash if itrsquos some other kind of Node then do that
clonendash But the Node doesnrsquot know all the other classes
that extend it
bull Reflection can be used to obtain information about a class its members or its methods
CET230 -- Razdan et al 20
Reflection cont
bull The Class class (see javalang) has methods that enable us to get information about the classndash eg getMethod(String name Class
[] parameterTypes) returns ldquoMethodrdquo
bull The Method class (see javalangreflect) has methods that enable us to get information about the Method and even CALL the methodndash Object invoke(Object obj Object[] args)
CET230 -- Razdan et al 21
ldquoBionicrdquo Nodebull We can modify the Node clone as follows
Node nodeClonetry nodeClone = (Node) superclone() catch( CloneNotSupportedException e ) throw new CloneNotSupportedException()if( thisdata instanceof Cloneable ) try Class c = thisdatagetClass() Method m = cgetMethod( clone null )
nodeClonedata = minvoke( thisdata null ) catch( Exception e ) nodeClonedata = thisdata else nodeClonedata = thisdataif( thisnext = null ) nodeClonenext = (Node) thisnextclone()else nodeClonenext = nullreturn( nodeClone )
CET230 -- Razdan et al 22
Revisiting the String classbull Some useful String methods
ndash charAt( int index)
ndash indexOf( char ch )
ndash indexOf( String str )
ndash split( String regex )
ndash startsWith( String prefix )
ndash substring( int beginIndex int endIndex )
ndash toLowerCase()
ndash toUpperCase()
Note StringTokenizer is a legacy class that is retained for compatibility reasons although its use is discouraged in new code It is recommended that anyone seeking this functionality use the split method of String or the javautilregex package instead
CET230 -- Razdan et al 23
Using Files for IObull Using files for IO is similar to standard IObull For standard input you usually use
ndash InputStreamReaderndash BufferedReader
bull For standard output you usually usendash Systemoutprint or println
bull For file input you can usendash FileReaderndash BufferedReader
bull For file output you can usendash FileWriterndash BufferedWriter
CET230 -- Razdan et al 24
FileReader constructorFileReader
public FileReader(String fileName) throws FileNotFoundException
Creates a new FileReader given the name of the file to read from
Parameters fileName - the name of the file to read from
Throws FileNotFoundException - if the named file does not exist is a directory rather than a regular file or for some other reason cannot be opened for reading
CET230 -- Razdan et al 25
Read ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )
String s = inreadLine()int i = 1while( s = null )
Systemoutprintln(ldquoLine ldquo + i + ldquo ldquo + s )
i++s = inreadLine()
inclose()
CET230 -- Razdan et al 26
FileWriter constructor
FileWriter
public FileWriter(String fileName) throws IOException Constructs a FileWriter object given a file name
Parameters fileName - String The system-dependent filename
Throws IOException - if the named file exists but is a directory rather than a regular file does not exist but cannot be created or cannot be opened for any other reason
CET230 -- Razdan et al 27
BufferedWriter
Method Summary void
close() Close the stream
voidflush() Flush the stream
voidnewLine() Write a line separator
voidwrite(char[] cbuf int off int len) Write a portion of an array of characters
voidwrite(int c) Write a single character
voidwrite(String s int off int len) Write a portion of a String
CET230 -- Razdan et al 28
Write ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )BufferedWriter out = new BufferedWriter(
new FileWriter(outfile) )
String s = inreadLine()while( s = null )
outwrite((ssplit(ldquosrdquo))[0])outnewLine()s = inreadLine()
inclose()outclose()
CET230 -- Razdan et al 29
Java Interfaces
bull A Java interface is a set of related methods that a programmer may want to support in a single classndash Eg Cloneablendash Eg Comparablehttpjavasuncomj2se150docsapijavalangComparablehtml
CET230 -- Razdan et al 30
Iterator Pattern
bull Motivation ndash an aggregate object should give you a way to access its
elements without exposing its internal structure
ndash Use of the object may want to traverse the object in many different ways ndash donrsquot want to bloat the interface with may traversal methods even if you could anticipate all the methods needed
ndash May need to have more than one traversal pending on the aggregate at once
CET230 -- Razdan et al 31
Iterator Patternbull Key idea take responsibility for access and
traversal out of the object and put it into an iterator object
bull Iterator provides basic ldquonavigationrdquo methods eg ndash Firstndash Nextndash IsDonendash CurrentItem
CET230 -- Razdan et al 32
Map Interface
bull A map is a collection class in which keyvalue pairs may be added A pair can be retrieved or removed by specifying just its key
CET230 -- Razdan et al 33
TreeMap
bull Javarsquos TreeMapltK Vgt implements the map interface in an efficient way in which the keys are required to come from a class (such as String) that implements the Comparable interface
CET230 -- Razdan et al 34
Example
bull From package javautil
bull TreeMapltString Integergt frequencyData
bull String word
bull Integer count
CET230 -- Razdan et al 35
Operations
bull public V get(K key)
bull public V put(K key V value)
bull public boolean containsKey(K key)
bull public SetltKgt keySet()
bull public int size()
bull public void clear()
CET230 -- Razdan et al 36
Iteration
for (String word wordMapkeySet())
hellipprocess this key which is in variable wordhellip
CET230 -- Razdan et al 12
Doubly Linked Listbull A doubly linked list allows us to store
references to the next node as well as the previous node
3 2 7 11
headtail
CET230 -- Razdan et al 13
Inheritance
bull A Doubly Linked List ldquois-ardquo List So we should take advantage of the List wersquove already implementedndash DoubleNode extends Nodendash DoubleList extends List
CET230 -- Razdan et al 14
Other Lists
bull Other types of lists are usefulndash Ordered list (elements in list are stored in some
order) Eg numbers are in increasing order strings are in alphabetical order etc
ndash Circular List the ldquoendrdquo of the list refers back to the head
ndash Skip Lists
CET230 -- Razdan et al 15
SkipList example from httpepaperpresscom
CET230 -- Razdan et al 16
Abstract Classesbull A robust implementation for List is to have an
ldquoAbstractListrdquo class from which concrete Lists (Singly Linked Doubly Linked Ordered etc) can be derived
bull An abstract classndash Has at least one abstract method (a method whose
interface is defined but NO implementation is specified by the class)
ndash Cannot be instantiatedndash Can provide implementation for some methodsndash Can provide attributes common to all concrete
subclasses
CET230 -- Razdan et al 17
Abstract List
bull Attributesndash head tail length
bull Methodsndash Constructor getLength equals clone
bull Abstract Methodsndash Add remove clone
CET230 -- Razdan et al 18
Implement clone in AbstractList
bull What Irsquod really like is to implement the clone() in the AbstractList classndash All Lists contain Nodes We donrsquot want to
rewrite the same code for the clone method over and over again in the concrete List classes
ndash Problem what about a DoubleList that contains DoubleNode The AbstractList implementation will not do enoughbecause the Node clone does not do enough
ndash But I WANT it to do enough
CET230 -- Razdan et al 19
Reflectionbull What if we made the Node clone ldquosmarterrdquo
ndash if itrsquos just a Node then do a Node clonendash if itrsquos some other kind of Node then do that
clonendash But the Node doesnrsquot know all the other classes
that extend it
bull Reflection can be used to obtain information about a class its members or its methods
CET230 -- Razdan et al 20
Reflection cont
bull The Class class (see javalang) has methods that enable us to get information about the classndash eg getMethod(String name Class
[] parameterTypes) returns ldquoMethodrdquo
bull The Method class (see javalangreflect) has methods that enable us to get information about the Method and even CALL the methodndash Object invoke(Object obj Object[] args)
CET230 -- Razdan et al 21
ldquoBionicrdquo Nodebull We can modify the Node clone as follows
Node nodeClonetry nodeClone = (Node) superclone() catch( CloneNotSupportedException e ) throw new CloneNotSupportedException()if( thisdata instanceof Cloneable ) try Class c = thisdatagetClass() Method m = cgetMethod( clone null )
nodeClonedata = minvoke( thisdata null ) catch( Exception e ) nodeClonedata = thisdata else nodeClonedata = thisdataif( thisnext = null ) nodeClonenext = (Node) thisnextclone()else nodeClonenext = nullreturn( nodeClone )
CET230 -- Razdan et al 22
Revisiting the String classbull Some useful String methods
ndash charAt( int index)
ndash indexOf( char ch )
ndash indexOf( String str )
ndash split( String regex )
ndash startsWith( String prefix )
ndash substring( int beginIndex int endIndex )
ndash toLowerCase()
ndash toUpperCase()
Note StringTokenizer is a legacy class that is retained for compatibility reasons although its use is discouraged in new code It is recommended that anyone seeking this functionality use the split method of String or the javautilregex package instead
CET230 -- Razdan et al 23
Using Files for IObull Using files for IO is similar to standard IObull For standard input you usually use
ndash InputStreamReaderndash BufferedReader
bull For standard output you usually usendash Systemoutprint or println
bull For file input you can usendash FileReaderndash BufferedReader
bull For file output you can usendash FileWriterndash BufferedWriter
CET230 -- Razdan et al 24
FileReader constructorFileReader
public FileReader(String fileName) throws FileNotFoundException
Creates a new FileReader given the name of the file to read from
Parameters fileName - the name of the file to read from
Throws FileNotFoundException - if the named file does not exist is a directory rather than a regular file or for some other reason cannot be opened for reading
CET230 -- Razdan et al 25
Read ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )
String s = inreadLine()int i = 1while( s = null )
Systemoutprintln(ldquoLine ldquo + i + ldquo ldquo + s )
i++s = inreadLine()
inclose()
CET230 -- Razdan et al 26
FileWriter constructor
FileWriter
public FileWriter(String fileName) throws IOException Constructs a FileWriter object given a file name
Parameters fileName - String The system-dependent filename
Throws IOException - if the named file exists but is a directory rather than a regular file does not exist but cannot be created or cannot be opened for any other reason
CET230 -- Razdan et al 27
BufferedWriter
Method Summary void
close() Close the stream
voidflush() Flush the stream
voidnewLine() Write a line separator
voidwrite(char[] cbuf int off int len) Write a portion of an array of characters
voidwrite(int c) Write a single character
voidwrite(String s int off int len) Write a portion of a String
CET230 -- Razdan et al 28
Write ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )BufferedWriter out = new BufferedWriter(
new FileWriter(outfile) )
String s = inreadLine()while( s = null )
outwrite((ssplit(ldquosrdquo))[0])outnewLine()s = inreadLine()
inclose()outclose()
CET230 -- Razdan et al 29
Java Interfaces
bull A Java interface is a set of related methods that a programmer may want to support in a single classndash Eg Cloneablendash Eg Comparablehttpjavasuncomj2se150docsapijavalangComparablehtml
CET230 -- Razdan et al 30
Iterator Pattern
bull Motivation ndash an aggregate object should give you a way to access its
elements without exposing its internal structure
ndash Use of the object may want to traverse the object in many different ways ndash donrsquot want to bloat the interface with may traversal methods even if you could anticipate all the methods needed
ndash May need to have more than one traversal pending on the aggregate at once
CET230 -- Razdan et al 31
Iterator Patternbull Key idea take responsibility for access and
traversal out of the object and put it into an iterator object
bull Iterator provides basic ldquonavigationrdquo methods eg ndash Firstndash Nextndash IsDonendash CurrentItem
CET230 -- Razdan et al 32
Map Interface
bull A map is a collection class in which keyvalue pairs may be added A pair can be retrieved or removed by specifying just its key
CET230 -- Razdan et al 33
TreeMap
bull Javarsquos TreeMapltK Vgt implements the map interface in an efficient way in which the keys are required to come from a class (such as String) that implements the Comparable interface
CET230 -- Razdan et al 34
Example
bull From package javautil
bull TreeMapltString Integergt frequencyData
bull String word
bull Integer count
CET230 -- Razdan et al 35
Operations
bull public V get(K key)
bull public V put(K key V value)
bull public boolean containsKey(K key)
bull public SetltKgt keySet()
bull public int size()
bull public void clear()
CET230 -- Razdan et al 36
Iteration
for (String word wordMapkeySet())
hellipprocess this key which is in variable wordhellip
CET230 -- Razdan et al 13
Inheritance
bull A Doubly Linked List ldquois-ardquo List So we should take advantage of the List wersquove already implementedndash DoubleNode extends Nodendash DoubleList extends List
CET230 -- Razdan et al 14
Other Lists
bull Other types of lists are usefulndash Ordered list (elements in list are stored in some
order) Eg numbers are in increasing order strings are in alphabetical order etc
ndash Circular List the ldquoendrdquo of the list refers back to the head
ndash Skip Lists
CET230 -- Razdan et al 15
SkipList example from httpepaperpresscom
CET230 -- Razdan et al 16
Abstract Classesbull A robust implementation for List is to have an
ldquoAbstractListrdquo class from which concrete Lists (Singly Linked Doubly Linked Ordered etc) can be derived
bull An abstract classndash Has at least one abstract method (a method whose
interface is defined but NO implementation is specified by the class)
ndash Cannot be instantiatedndash Can provide implementation for some methodsndash Can provide attributes common to all concrete
subclasses
CET230 -- Razdan et al 17
Abstract List
bull Attributesndash head tail length
bull Methodsndash Constructor getLength equals clone
bull Abstract Methodsndash Add remove clone
CET230 -- Razdan et al 18
Implement clone in AbstractList
bull What Irsquod really like is to implement the clone() in the AbstractList classndash All Lists contain Nodes We donrsquot want to
rewrite the same code for the clone method over and over again in the concrete List classes
ndash Problem what about a DoubleList that contains DoubleNode The AbstractList implementation will not do enoughbecause the Node clone does not do enough
ndash But I WANT it to do enough
CET230 -- Razdan et al 19
Reflectionbull What if we made the Node clone ldquosmarterrdquo
ndash if itrsquos just a Node then do a Node clonendash if itrsquos some other kind of Node then do that
clonendash But the Node doesnrsquot know all the other classes
that extend it
bull Reflection can be used to obtain information about a class its members or its methods
CET230 -- Razdan et al 20
Reflection cont
bull The Class class (see javalang) has methods that enable us to get information about the classndash eg getMethod(String name Class
[] parameterTypes) returns ldquoMethodrdquo
bull The Method class (see javalangreflect) has methods that enable us to get information about the Method and even CALL the methodndash Object invoke(Object obj Object[] args)
CET230 -- Razdan et al 21
ldquoBionicrdquo Nodebull We can modify the Node clone as follows
Node nodeClonetry nodeClone = (Node) superclone() catch( CloneNotSupportedException e ) throw new CloneNotSupportedException()if( thisdata instanceof Cloneable ) try Class c = thisdatagetClass() Method m = cgetMethod( clone null )
nodeClonedata = minvoke( thisdata null ) catch( Exception e ) nodeClonedata = thisdata else nodeClonedata = thisdataif( thisnext = null ) nodeClonenext = (Node) thisnextclone()else nodeClonenext = nullreturn( nodeClone )
CET230 -- Razdan et al 22
Revisiting the String classbull Some useful String methods
ndash charAt( int index)
ndash indexOf( char ch )
ndash indexOf( String str )
ndash split( String regex )
ndash startsWith( String prefix )
ndash substring( int beginIndex int endIndex )
ndash toLowerCase()
ndash toUpperCase()
Note StringTokenizer is a legacy class that is retained for compatibility reasons although its use is discouraged in new code It is recommended that anyone seeking this functionality use the split method of String or the javautilregex package instead
CET230 -- Razdan et al 23
Using Files for IObull Using files for IO is similar to standard IObull For standard input you usually use
ndash InputStreamReaderndash BufferedReader
bull For standard output you usually usendash Systemoutprint or println
bull For file input you can usendash FileReaderndash BufferedReader
bull For file output you can usendash FileWriterndash BufferedWriter
CET230 -- Razdan et al 24
FileReader constructorFileReader
public FileReader(String fileName) throws FileNotFoundException
Creates a new FileReader given the name of the file to read from
Parameters fileName - the name of the file to read from
Throws FileNotFoundException - if the named file does not exist is a directory rather than a regular file or for some other reason cannot be opened for reading
CET230 -- Razdan et al 25
Read ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )
String s = inreadLine()int i = 1while( s = null )
Systemoutprintln(ldquoLine ldquo + i + ldquo ldquo + s )
i++s = inreadLine()
inclose()
CET230 -- Razdan et al 26
FileWriter constructor
FileWriter
public FileWriter(String fileName) throws IOException Constructs a FileWriter object given a file name
Parameters fileName - String The system-dependent filename
Throws IOException - if the named file exists but is a directory rather than a regular file does not exist but cannot be created or cannot be opened for any other reason
CET230 -- Razdan et al 27
BufferedWriter
Method Summary void
close() Close the stream
voidflush() Flush the stream
voidnewLine() Write a line separator
voidwrite(char[] cbuf int off int len) Write a portion of an array of characters
voidwrite(int c) Write a single character
voidwrite(String s int off int len) Write a portion of a String
CET230 -- Razdan et al 28
Write ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )BufferedWriter out = new BufferedWriter(
new FileWriter(outfile) )
String s = inreadLine()while( s = null )
outwrite((ssplit(ldquosrdquo))[0])outnewLine()s = inreadLine()
inclose()outclose()
CET230 -- Razdan et al 29
Java Interfaces
bull A Java interface is a set of related methods that a programmer may want to support in a single classndash Eg Cloneablendash Eg Comparablehttpjavasuncomj2se150docsapijavalangComparablehtml
CET230 -- Razdan et al 30
Iterator Pattern
bull Motivation ndash an aggregate object should give you a way to access its
elements without exposing its internal structure
ndash Use of the object may want to traverse the object in many different ways ndash donrsquot want to bloat the interface with may traversal methods even if you could anticipate all the methods needed
ndash May need to have more than one traversal pending on the aggregate at once
CET230 -- Razdan et al 31
Iterator Patternbull Key idea take responsibility for access and
traversal out of the object and put it into an iterator object
bull Iterator provides basic ldquonavigationrdquo methods eg ndash Firstndash Nextndash IsDonendash CurrentItem
CET230 -- Razdan et al 32
Map Interface
bull A map is a collection class in which keyvalue pairs may be added A pair can be retrieved or removed by specifying just its key
CET230 -- Razdan et al 33
TreeMap
bull Javarsquos TreeMapltK Vgt implements the map interface in an efficient way in which the keys are required to come from a class (such as String) that implements the Comparable interface
CET230 -- Razdan et al 34
Example
bull From package javautil
bull TreeMapltString Integergt frequencyData
bull String word
bull Integer count
CET230 -- Razdan et al 35
Operations
bull public V get(K key)
bull public V put(K key V value)
bull public boolean containsKey(K key)
bull public SetltKgt keySet()
bull public int size()
bull public void clear()
CET230 -- Razdan et al 36
Iteration
for (String word wordMapkeySet())
hellipprocess this key which is in variable wordhellip
CET230 -- Razdan et al 14
Other Lists
bull Other types of lists are usefulndash Ordered list (elements in list are stored in some
order) Eg numbers are in increasing order strings are in alphabetical order etc
ndash Circular List the ldquoendrdquo of the list refers back to the head
ndash Skip Lists
CET230 -- Razdan et al 15
SkipList example from httpepaperpresscom
CET230 -- Razdan et al 16
Abstract Classesbull A robust implementation for List is to have an
ldquoAbstractListrdquo class from which concrete Lists (Singly Linked Doubly Linked Ordered etc) can be derived
bull An abstract classndash Has at least one abstract method (a method whose
interface is defined but NO implementation is specified by the class)
ndash Cannot be instantiatedndash Can provide implementation for some methodsndash Can provide attributes common to all concrete
subclasses
CET230 -- Razdan et al 17
Abstract List
bull Attributesndash head tail length
bull Methodsndash Constructor getLength equals clone
bull Abstract Methodsndash Add remove clone
CET230 -- Razdan et al 18
Implement clone in AbstractList
bull What Irsquod really like is to implement the clone() in the AbstractList classndash All Lists contain Nodes We donrsquot want to
rewrite the same code for the clone method over and over again in the concrete List classes
ndash Problem what about a DoubleList that contains DoubleNode The AbstractList implementation will not do enoughbecause the Node clone does not do enough
ndash But I WANT it to do enough
CET230 -- Razdan et al 19
Reflectionbull What if we made the Node clone ldquosmarterrdquo
ndash if itrsquos just a Node then do a Node clonendash if itrsquos some other kind of Node then do that
clonendash But the Node doesnrsquot know all the other classes
that extend it
bull Reflection can be used to obtain information about a class its members or its methods
CET230 -- Razdan et al 20
Reflection cont
bull The Class class (see javalang) has methods that enable us to get information about the classndash eg getMethod(String name Class
[] parameterTypes) returns ldquoMethodrdquo
bull The Method class (see javalangreflect) has methods that enable us to get information about the Method and even CALL the methodndash Object invoke(Object obj Object[] args)
CET230 -- Razdan et al 21
ldquoBionicrdquo Nodebull We can modify the Node clone as follows
Node nodeClonetry nodeClone = (Node) superclone() catch( CloneNotSupportedException e ) throw new CloneNotSupportedException()if( thisdata instanceof Cloneable ) try Class c = thisdatagetClass() Method m = cgetMethod( clone null )
nodeClonedata = minvoke( thisdata null ) catch( Exception e ) nodeClonedata = thisdata else nodeClonedata = thisdataif( thisnext = null ) nodeClonenext = (Node) thisnextclone()else nodeClonenext = nullreturn( nodeClone )
CET230 -- Razdan et al 22
Revisiting the String classbull Some useful String methods
ndash charAt( int index)
ndash indexOf( char ch )
ndash indexOf( String str )
ndash split( String regex )
ndash startsWith( String prefix )
ndash substring( int beginIndex int endIndex )
ndash toLowerCase()
ndash toUpperCase()
Note StringTokenizer is a legacy class that is retained for compatibility reasons although its use is discouraged in new code It is recommended that anyone seeking this functionality use the split method of String or the javautilregex package instead
CET230 -- Razdan et al 23
Using Files for IObull Using files for IO is similar to standard IObull For standard input you usually use
ndash InputStreamReaderndash BufferedReader
bull For standard output you usually usendash Systemoutprint or println
bull For file input you can usendash FileReaderndash BufferedReader
bull For file output you can usendash FileWriterndash BufferedWriter
CET230 -- Razdan et al 24
FileReader constructorFileReader
public FileReader(String fileName) throws FileNotFoundException
Creates a new FileReader given the name of the file to read from
Parameters fileName - the name of the file to read from
Throws FileNotFoundException - if the named file does not exist is a directory rather than a regular file or for some other reason cannot be opened for reading
CET230 -- Razdan et al 25
Read ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )
String s = inreadLine()int i = 1while( s = null )
Systemoutprintln(ldquoLine ldquo + i + ldquo ldquo + s )
i++s = inreadLine()
inclose()
CET230 -- Razdan et al 26
FileWriter constructor
FileWriter
public FileWriter(String fileName) throws IOException Constructs a FileWriter object given a file name
Parameters fileName - String The system-dependent filename
Throws IOException - if the named file exists but is a directory rather than a regular file does not exist but cannot be created or cannot be opened for any other reason
CET230 -- Razdan et al 27
BufferedWriter
Method Summary void
close() Close the stream
voidflush() Flush the stream
voidnewLine() Write a line separator
voidwrite(char[] cbuf int off int len) Write a portion of an array of characters
voidwrite(int c) Write a single character
voidwrite(String s int off int len) Write a portion of a String
CET230 -- Razdan et al 28
Write ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )BufferedWriter out = new BufferedWriter(
new FileWriter(outfile) )
String s = inreadLine()while( s = null )
outwrite((ssplit(ldquosrdquo))[0])outnewLine()s = inreadLine()
inclose()outclose()
CET230 -- Razdan et al 29
Java Interfaces
bull A Java interface is a set of related methods that a programmer may want to support in a single classndash Eg Cloneablendash Eg Comparablehttpjavasuncomj2se150docsapijavalangComparablehtml
CET230 -- Razdan et al 30
Iterator Pattern
bull Motivation ndash an aggregate object should give you a way to access its
elements without exposing its internal structure
ndash Use of the object may want to traverse the object in many different ways ndash donrsquot want to bloat the interface with may traversal methods even if you could anticipate all the methods needed
ndash May need to have more than one traversal pending on the aggregate at once
CET230 -- Razdan et al 31
Iterator Patternbull Key idea take responsibility for access and
traversal out of the object and put it into an iterator object
bull Iterator provides basic ldquonavigationrdquo methods eg ndash Firstndash Nextndash IsDonendash CurrentItem
CET230 -- Razdan et al 32
Map Interface
bull A map is a collection class in which keyvalue pairs may be added A pair can be retrieved or removed by specifying just its key
CET230 -- Razdan et al 33
TreeMap
bull Javarsquos TreeMapltK Vgt implements the map interface in an efficient way in which the keys are required to come from a class (such as String) that implements the Comparable interface
CET230 -- Razdan et al 34
Example
bull From package javautil
bull TreeMapltString Integergt frequencyData
bull String word
bull Integer count
CET230 -- Razdan et al 35
Operations
bull public V get(K key)
bull public V put(K key V value)
bull public boolean containsKey(K key)
bull public SetltKgt keySet()
bull public int size()
bull public void clear()
CET230 -- Razdan et al 36
Iteration
for (String word wordMapkeySet())
hellipprocess this key which is in variable wordhellip
CET230 -- Razdan et al 15
SkipList example from httpepaperpresscom
CET230 -- Razdan et al 16
Abstract Classesbull A robust implementation for List is to have an
ldquoAbstractListrdquo class from which concrete Lists (Singly Linked Doubly Linked Ordered etc) can be derived
bull An abstract classndash Has at least one abstract method (a method whose
interface is defined but NO implementation is specified by the class)
ndash Cannot be instantiatedndash Can provide implementation for some methodsndash Can provide attributes common to all concrete
subclasses
CET230 -- Razdan et al 17
Abstract List
bull Attributesndash head tail length
bull Methodsndash Constructor getLength equals clone
bull Abstract Methodsndash Add remove clone
CET230 -- Razdan et al 18
Implement clone in AbstractList
bull What Irsquod really like is to implement the clone() in the AbstractList classndash All Lists contain Nodes We donrsquot want to
rewrite the same code for the clone method over and over again in the concrete List classes
ndash Problem what about a DoubleList that contains DoubleNode The AbstractList implementation will not do enoughbecause the Node clone does not do enough
ndash But I WANT it to do enough
CET230 -- Razdan et al 19
Reflectionbull What if we made the Node clone ldquosmarterrdquo
ndash if itrsquos just a Node then do a Node clonendash if itrsquos some other kind of Node then do that
clonendash But the Node doesnrsquot know all the other classes
that extend it
bull Reflection can be used to obtain information about a class its members or its methods
CET230 -- Razdan et al 20
Reflection cont
bull The Class class (see javalang) has methods that enable us to get information about the classndash eg getMethod(String name Class
[] parameterTypes) returns ldquoMethodrdquo
bull The Method class (see javalangreflect) has methods that enable us to get information about the Method and even CALL the methodndash Object invoke(Object obj Object[] args)
CET230 -- Razdan et al 21
ldquoBionicrdquo Nodebull We can modify the Node clone as follows
Node nodeClonetry nodeClone = (Node) superclone() catch( CloneNotSupportedException e ) throw new CloneNotSupportedException()if( thisdata instanceof Cloneable ) try Class c = thisdatagetClass() Method m = cgetMethod( clone null )
nodeClonedata = minvoke( thisdata null ) catch( Exception e ) nodeClonedata = thisdata else nodeClonedata = thisdataif( thisnext = null ) nodeClonenext = (Node) thisnextclone()else nodeClonenext = nullreturn( nodeClone )
CET230 -- Razdan et al 22
Revisiting the String classbull Some useful String methods
ndash charAt( int index)
ndash indexOf( char ch )
ndash indexOf( String str )
ndash split( String regex )
ndash startsWith( String prefix )
ndash substring( int beginIndex int endIndex )
ndash toLowerCase()
ndash toUpperCase()
Note StringTokenizer is a legacy class that is retained for compatibility reasons although its use is discouraged in new code It is recommended that anyone seeking this functionality use the split method of String or the javautilregex package instead
CET230 -- Razdan et al 23
Using Files for IObull Using files for IO is similar to standard IObull For standard input you usually use
ndash InputStreamReaderndash BufferedReader
bull For standard output you usually usendash Systemoutprint or println
bull For file input you can usendash FileReaderndash BufferedReader
bull For file output you can usendash FileWriterndash BufferedWriter
CET230 -- Razdan et al 24
FileReader constructorFileReader
public FileReader(String fileName) throws FileNotFoundException
Creates a new FileReader given the name of the file to read from
Parameters fileName - the name of the file to read from
Throws FileNotFoundException - if the named file does not exist is a directory rather than a regular file or for some other reason cannot be opened for reading
CET230 -- Razdan et al 25
Read ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )
String s = inreadLine()int i = 1while( s = null )
Systemoutprintln(ldquoLine ldquo + i + ldquo ldquo + s )
i++s = inreadLine()
inclose()
CET230 -- Razdan et al 26
FileWriter constructor
FileWriter
public FileWriter(String fileName) throws IOException Constructs a FileWriter object given a file name
Parameters fileName - String The system-dependent filename
Throws IOException - if the named file exists but is a directory rather than a regular file does not exist but cannot be created or cannot be opened for any other reason
CET230 -- Razdan et al 27
BufferedWriter
Method Summary void
close() Close the stream
voidflush() Flush the stream
voidnewLine() Write a line separator
voidwrite(char[] cbuf int off int len) Write a portion of an array of characters
voidwrite(int c) Write a single character
voidwrite(String s int off int len) Write a portion of a String
CET230 -- Razdan et al 28
Write ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )BufferedWriter out = new BufferedWriter(
new FileWriter(outfile) )
String s = inreadLine()while( s = null )
outwrite((ssplit(ldquosrdquo))[0])outnewLine()s = inreadLine()
inclose()outclose()
CET230 -- Razdan et al 29
Java Interfaces
bull A Java interface is a set of related methods that a programmer may want to support in a single classndash Eg Cloneablendash Eg Comparablehttpjavasuncomj2se150docsapijavalangComparablehtml
CET230 -- Razdan et al 30
Iterator Pattern
bull Motivation ndash an aggregate object should give you a way to access its
elements without exposing its internal structure
ndash Use of the object may want to traverse the object in many different ways ndash donrsquot want to bloat the interface with may traversal methods even if you could anticipate all the methods needed
ndash May need to have more than one traversal pending on the aggregate at once
CET230 -- Razdan et al 31
Iterator Patternbull Key idea take responsibility for access and
traversal out of the object and put it into an iterator object
bull Iterator provides basic ldquonavigationrdquo methods eg ndash Firstndash Nextndash IsDonendash CurrentItem
CET230 -- Razdan et al 32
Map Interface
bull A map is a collection class in which keyvalue pairs may be added A pair can be retrieved or removed by specifying just its key
CET230 -- Razdan et al 33
TreeMap
bull Javarsquos TreeMapltK Vgt implements the map interface in an efficient way in which the keys are required to come from a class (such as String) that implements the Comparable interface
CET230 -- Razdan et al 34
Example
bull From package javautil
bull TreeMapltString Integergt frequencyData
bull String word
bull Integer count
CET230 -- Razdan et al 35
Operations
bull public V get(K key)
bull public V put(K key V value)
bull public boolean containsKey(K key)
bull public SetltKgt keySet()
bull public int size()
bull public void clear()
CET230 -- Razdan et al 36
Iteration
for (String word wordMapkeySet())
hellipprocess this key which is in variable wordhellip
CET230 -- Razdan et al 16
Abstract Classesbull A robust implementation for List is to have an
ldquoAbstractListrdquo class from which concrete Lists (Singly Linked Doubly Linked Ordered etc) can be derived
bull An abstract classndash Has at least one abstract method (a method whose
interface is defined but NO implementation is specified by the class)
ndash Cannot be instantiatedndash Can provide implementation for some methodsndash Can provide attributes common to all concrete
subclasses
CET230 -- Razdan et al 17
Abstract List
bull Attributesndash head tail length
bull Methodsndash Constructor getLength equals clone
bull Abstract Methodsndash Add remove clone
CET230 -- Razdan et al 18
Implement clone in AbstractList
bull What Irsquod really like is to implement the clone() in the AbstractList classndash All Lists contain Nodes We donrsquot want to
rewrite the same code for the clone method over and over again in the concrete List classes
ndash Problem what about a DoubleList that contains DoubleNode The AbstractList implementation will not do enoughbecause the Node clone does not do enough
ndash But I WANT it to do enough
CET230 -- Razdan et al 19
Reflectionbull What if we made the Node clone ldquosmarterrdquo
ndash if itrsquos just a Node then do a Node clonendash if itrsquos some other kind of Node then do that
clonendash But the Node doesnrsquot know all the other classes
that extend it
bull Reflection can be used to obtain information about a class its members or its methods
CET230 -- Razdan et al 20
Reflection cont
bull The Class class (see javalang) has methods that enable us to get information about the classndash eg getMethod(String name Class
[] parameterTypes) returns ldquoMethodrdquo
bull The Method class (see javalangreflect) has methods that enable us to get information about the Method and even CALL the methodndash Object invoke(Object obj Object[] args)
CET230 -- Razdan et al 21
ldquoBionicrdquo Nodebull We can modify the Node clone as follows
Node nodeClonetry nodeClone = (Node) superclone() catch( CloneNotSupportedException e ) throw new CloneNotSupportedException()if( thisdata instanceof Cloneable ) try Class c = thisdatagetClass() Method m = cgetMethod( clone null )
nodeClonedata = minvoke( thisdata null ) catch( Exception e ) nodeClonedata = thisdata else nodeClonedata = thisdataif( thisnext = null ) nodeClonenext = (Node) thisnextclone()else nodeClonenext = nullreturn( nodeClone )
CET230 -- Razdan et al 22
Revisiting the String classbull Some useful String methods
ndash charAt( int index)
ndash indexOf( char ch )
ndash indexOf( String str )
ndash split( String regex )
ndash startsWith( String prefix )
ndash substring( int beginIndex int endIndex )
ndash toLowerCase()
ndash toUpperCase()
Note StringTokenizer is a legacy class that is retained for compatibility reasons although its use is discouraged in new code It is recommended that anyone seeking this functionality use the split method of String or the javautilregex package instead
CET230 -- Razdan et al 23
Using Files for IObull Using files for IO is similar to standard IObull For standard input you usually use
ndash InputStreamReaderndash BufferedReader
bull For standard output you usually usendash Systemoutprint or println
bull For file input you can usendash FileReaderndash BufferedReader
bull For file output you can usendash FileWriterndash BufferedWriter
CET230 -- Razdan et al 24
FileReader constructorFileReader
public FileReader(String fileName) throws FileNotFoundException
Creates a new FileReader given the name of the file to read from
Parameters fileName - the name of the file to read from
Throws FileNotFoundException - if the named file does not exist is a directory rather than a regular file or for some other reason cannot be opened for reading
CET230 -- Razdan et al 25
Read ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )
String s = inreadLine()int i = 1while( s = null )
Systemoutprintln(ldquoLine ldquo + i + ldquo ldquo + s )
i++s = inreadLine()
inclose()
CET230 -- Razdan et al 26
FileWriter constructor
FileWriter
public FileWriter(String fileName) throws IOException Constructs a FileWriter object given a file name
Parameters fileName - String The system-dependent filename
Throws IOException - if the named file exists but is a directory rather than a regular file does not exist but cannot be created or cannot be opened for any other reason
CET230 -- Razdan et al 27
BufferedWriter
Method Summary void
close() Close the stream
voidflush() Flush the stream
voidnewLine() Write a line separator
voidwrite(char[] cbuf int off int len) Write a portion of an array of characters
voidwrite(int c) Write a single character
voidwrite(String s int off int len) Write a portion of a String
CET230 -- Razdan et al 28
Write ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )BufferedWriter out = new BufferedWriter(
new FileWriter(outfile) )
String s = inreadLine()while( s = null )
outwrite((ssplit(ldquosrdquo))[0])outnewLine()s = inreadLine()
inclose()outclose()
CET230 -- Razdan et al 29
Java Interfaces
bull A Java interface is a set of related methods that a programmer may want to support in a single classndash Eg Cloneablendash Eg Comparablehttpjavasuncomj2se150docsapijavalangComparablehtml
CET230 -- Razdan et al 30
Iterator Pattern
bull Motivation ndash an aggregate object should give you a way to access its
elements without exposing its internal structure
ndash Use of the object may want to traverse the object in many different ways ndash donrsquot want to bloat the interface with may traversal methods even if you could anticipate all the methods needed
ndash May need to have more than one traversal pending on the aggregate at once
CET230 -- Razdan et al 31
Iterator Patternbull Key idea take responsibility for access and
traversal out of the object and put it into an iterator object
bull Iterator provides basic ldquonavigationrdquo methods eg ndash Firstndash Nextndash IsDonendash CurrentItem
CET230 -- Razdan et al 32
Map Interface
bull A map is a collection class in which keyvalue pairs may be added A pair can be retrieved or removed by specifying just its key
CET230 -- Razdan et al 33
TreeMap
bull Javarsquos TreeMapltK Vgt implements the map interface in an efficient way in which the keys are required to come from a class (such as String) that implements the Comparable interface
CET230 -- Razdan et al 34
Example
bull From package javautil
bull TreeMapltString Integergt frequencyData
bull String word
bull Integer count
CET230 -- Razdan et al 35
Operations
bull public V get(K key)
bull public V put(K key V value)
bull public boolean containsKey(K key)
bull public SetltKgt keySet()
bull public int size()
bull public void clear()
CET230 -- Razdan et al 36
Iteration
for (String word wordMapkeySet())
hellipprocess this key which is in variable wordhellip
CET230 -- Razdan et al 17
Abstract List
bull Attributesndash head tail length
bull Methodsndash Constructor getLength equals clone
bull Abstract Methodsndash Add remove clone
CET230 -- Razdan et al 18
Implement clone in AbstractList
bull What Irsquod really like is to implement the clone() in the AbstractList classndash All Lists contain Nodes We donrsquot want to
rewrite the same code for the clone method over and over again in the concrete List classes
ndash Problem what about a DoubleList that contains DoubleNode The AbstractList implementation will not do enoughbecause the Node clone does not do enough
ndash But I WANT it to do enough
CET230 -- Razdan et al 19
Reflectionbull What if we made the Node clone ldquosmarterrdquo
ndash if itrsquos just a Node then do a Node clonendash if itrsquos some other kind of Node then do that
clonendash But the Node doesnrsquot know all the other classes
that extend it
bull Reflection can be used to obtain information about a class its members or its methods
CET230 -- Razdan et al 20
Reflection cont
bull The Class class (see javalang) has methods that enable us to get information about the classndash eg getMethod(String name Class
[] parameterTypes) returns ldquoMethodrdquo
bull The Method class (see javalangreflect) has methods that enable us to get information about the Method and even CALL the methodndash Object invoke(Object obj Object[] args)
CET230 -- Razdan et al 21
ldquoBionicrdquo Nodebull We can modify the Node clone as follows
Node nodeClonetry nodeClone = (Node) superclone() catch( CloneNotSupportedException e ) throw new CloneNotSupportedException()if( thisdata instanceof Cloneable ) try Class c = thisdatagetClass() Method m = cgetMethod( clone null )
nodeClonedata = minvoke( thisdata null ) catch( Exception e ) nodeClonedata = thisdata else nodeClonedata = thisdataif( thisnext = null ) nodeClonenext = (Node) thisnextclone()else nodeClonenext = nullreturn( nodeClone )
CET230 -- Razdan et al 22
Revisiting the String classbull Some useful String methods
ndash charAt( int index)
ndash indexOf( char ch )
ndash indexOf( String str )
ndash split( String regex )
ndash startsWith( String prefix )
ndash substring( int beginIndex int endIndex )
ndash toLowerCase()
ndash toUpperCase()
Note StringTokenizer is a legacy class that is retained for compatibility reasons although its use is discouraged in new code It is recommended that anyone seeking this functionality use the split method of String or the javautilregex package instead
CET230 -- Razdan et al 23
Using Files for IObull Using files for IO is similar to standard IObull For standard input you usually use
ndash InputStreamReaderndash BufferedReader
bull For standard output you usually usendash Systemoutprint or println
bull For file input you can usendash FileReaderndash BufferedReader
bull For file output you can usendash FileWriterndash BufferedWriter
CET230 -- Razdan et al 24
FileReader constructorFileReader
public FileReader(String fileName) throws FileNotFoundException
Creates a new FileReader given the name of the file to read from
Parameters fileName - the name of the file to read from
Throws FileNotFoundException - if the named file does not exist is a directory rather than a regular file or for some other reason cannot be opened for reading
CET230 -- Razdan et al 25
Read ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )
String s = inreadLine()int i = 1while( s = null )
Systemoutprintln(ldquoLine ldquo + i + ldquo ldquo + s )
i++s = inreadLine()
inclose()
CET230 -- Razdan et al 26
FileWriter constructor
FileWriter
public FileWriter(String fileName) throws IOException Constructs a FileWriter object given a file name
Parameters fileName - String The system-dependent filename
Throws IOException - if the named file exists but is a directory rather than a regular file does not exist but cannot be created or cannot be opened for any other reason
CET230 -- Razdan et al 27
BufferedWriter
Method Summary void
close() Close the stream
voidflush() Flush the stream
voidnewLine() Write a line separator
voidwrite(char[] cbuf int off int len) Write a portion of an array of characters
voidwrite(int c) Write a single character
voidwrite(String s int off int len) Write a portion of a String
CET230 -- Razdan et al 28
Write ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )BufferedWriter out = new BufferedWriter(
new FileWriter(outfile) )
String s = inreadLine()while( s = null )
outwrite((ssplit(ldquosrdquo))[0])outnewLine()s = inreadLine()
inclose()outclose()
CET230 -- Razdan et al 29
Java Interfaces
bull A Java interface is a set of related methods that a programmer may want to support in a single classndash Eg Cloneablendash Eg Comparablehttpjavasuncomj2se150docsapijavalangComparablehtml
CET230 -- Razdan et al 30
Iterator Pattern
bull Motivation ndash an aggregate object should give you a way to access its
elements without exposing its internal structure
ndash Use of the object may want to traverse the object in many different ways ndash donrsquot want to bloat the interface with may traversal methods even if you could anticipate all the methods needed
ndash May need to have more than one traversal pending on the aggregate at once
CET230 -- Razdan et al 31
Iterator Patternbull Key idea take responsibility for access and
traversal out of the object and put it into an iterator object
bull Iterator provides basic ldquonavigationrdquo methods eg ndash Firstndash Nextndash IsDonendash CurrentItem
CET230 -- Razdan et al 32
Map Interface
bull A map is a collection class in which keyvalue pairs may be added A pair can be retrieved or removed by specifying just its key
CET230 -- Razdan et al 33
TreeMap
bull Javarsquos TreeMapltK Vgt implements the map interface in an efficient way in which the keys are required to come from a class (such as String) that implements the Comparable interface
CET230 -- Razdan et al 34
Example
bull From package javautil
bull TreeMapltString Integergt frequencyData
bull String word
bull Integer count
CET230 -- Razdan et al 35
Operations
bull public V get(K key)
bull public V put(K key V value)
bull public boolean containsKey(K key)
bull public SetltKgt keySet()
bull public int size()
bull public void clear()
CET230 -- Razdan et al 36
Iteration
for (String word wordMapkeySet())
hellipprocess this key which is in variable wordhellip
CET230 -- Razdan et al 18
Implement clone in AbstractList
bull What Irsquod really like is to implement the clone() in the AbstractList classndash All Lists contain Nodes We donrsquot want to
rewrite the same code for the clone method over and over again in the concrete List classes
ndash Problem what about a DoubleList that contains DoubleNode The AbstractList implementation will not do enoughbecause the Node clone does not do enough
ndash But I WANT it to do enough
CET230 -- Razdan et al 19
Reflectionbull What if we made the Node clone ldquosmarterrdquo
ndash if itrsquos just a Node then do a Node clonendash if itrsquos some other kind of Node then do that
clonendash But the Node doesnrsquot know all the other classes
that extend it
bull Reflection can be used to obtain information about a class its members or its methods
CET230 -- Razdan et al 20
Reflection cont
bull The Class class (see javalang) has methods that enable us to get information about the classndash eg getMethod(String name Class
[] parameterTypes) returns ldquoMethodrdquo
bull The Method class (see javalangreflect) has methods that enable us to get information about the Method and even CALL the methodndash Object invoke(Object obj Object[] args)
CET230 -- Razdan et al 21
ldquoBionicrdquo Nodebull We can modify the Node clone as follows
Node nodeClonetry nodeClone = (Node) superclone() catch( CloneNotSupportedException e ) throw new CloneNotSupportedException()if( thisdata instanceof Cloneable ) try Class c = thisdatagetClass() Method m = cgetMethod( clone null )
nodeClonedata = minvoke( thisdata null ) catch( Exception e ) nodeClonedata = thisdata else nodeClonedata = thisdataif( thisnext = null ) nodeClonenext = (Node) thisnextclone()else nodeClonenext = nullreturn( nodeClone )
CET230 -- Razdan et al 22
Revisiting the String classbull Some useful String methods
ndash charAt( int index)
ndash indexOf( char ch )
ndash indexOf( String str )
ndash split( String regex )
ndash startsWith( String prefix )
ndash substring( int beginIndex int endIndex )
ndash toLowerCase()
ndash toUpperCase()
Note StringTokenizer is a legacy class that is retained for compatibility reasons although its use is discouraged in new code It is recommended that anyone seeking this functionality use the split method of String or the javautilregex package instead
CET230 -- Razdan et al 23
Using Files for IObull Using files for IO is similar to standard IObull For standard input you usually use
ndash InputStreamReaderndash BufferedReader
bull For standard output you usually usendash Systemoutprint or println
bull For file input you can usendash FileReaderndash BufferedReader
bull For file output you can usendash FileWriterndash BufferedWriter
CET230 -- Razdan et al 24
FileReader constructorFileReader
public FileReader(String fileName) throws FileNotFoundException
Creates a new FileReader given the name of the file to read from
Parameters fileName - the name of the file to read from
Throws FileNotFoundException - if the named file does not exist is a directory rather than a regular file or for some other reason cannot be opened for reading
CET230 -- Razdan et al 25
Read ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )
String s = inreadLine()int i = 1while( s = null )
Systemoutprintln(ldquoLine ldquo + i + ldquo ldquo + s )
i++s = inreadLine()
inclose()
CET230 -- Razdan et al 26
FileWriter constructor
FileWriter
public FileWriter(String fileName) throws IOException Constructs a FileWriter object given a file name
Parameters fileName - String The system-dependent filename
Throws IOException - if the named file exists but is a directory rather than a regular file does not exist but cannot be created or cannot be opened for any other reason
CET230 -- Razdan et al 27
BufferedWriter
Method Summary void
close() Close the stream
voidflush() Flush the stream
voidnewLine() Write a line separator
voidwrite(char[] cbuf int off int len) Write a portion of an array of characters
voidwrite(int c) Write a single character
voidwrite(String s int off int len) Write a portion of a String
CET230 -- Razdan et al 28
Write ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )BufferedWriter out = new BufferedWriter(
new FileWriter(outfile) )
String s = inreadLine()while( s = null )
outwrite((ssplit(ldquosrdquo))[0])outnewLine()s = inreadLine()
inclose()outclose()
CET230 -- Razdan et al 29
Java Interfaces
bull A Java interface is a set of related methods that a programmer may want to support in a single classndash Eg Cloneablendash Eg Comparablehttpjavasuncomj2se150docsapijavalangComparablehtml
CET230 -- Razdan et al 30
Iterator Pattern
bull Motivation ndash an aggregate object should give you a way to access its
elements without exposing its internal structure
ndash Use of the object may want to traverse the object in many different ways ndash donrsquot want to bloat the interface with may traversal methods even if you could anticipate all the methods needed
ndash May need to have more than one traversal pending on the aggregate at once
CET230 -- Razdan et al 31
Iterator Patternbull Key idea take responsibility for access and
traversal out of the object and put it into an iterator object
bull Iterator provides basic ldquonavigationrdquo methods eg ndash Firstndash Nextndash IsDonendash CurrentItem
CET230 -- Razdan et al 32
Map Interface
bull A map is a collection class in which keyvalue pairs may be added A pair can be retrieved or removed by specifying just its key
CET230 -- Razdan et al 33
TreeMap
bull Javarsquos TreeMapltK Vgt implements the map interface in an efficient way in which the keys are required to come from a class (such as String) that implements the Comparable interface
CET230 -- Razdan et al 34
Example
bull From package javautil
bull TreeMapltString Integergt frequencyData
bull String word
bull Integer count
CET230 -- Razdan et al 35
Operations
bull public V get(K key)
bull public V put(K key V value)
bull public boolean containsKey(K key)
bull public SetltKgt keySet()
bull public int size()
bull public void clear()
CET230 -- Razdan et al 36
Iteration
for (String word wordMapkeySet())
hellipprocess this key which is in variable wordhellip
CET230 -- Razdan et al 19
Reflectionbull What if we made the Node clone ldquosmarterrdquo
ndash if itrsquos just a Node then do a Node clonendash if itrsquos some other kind of Node then do that
clonendash But the Node doesnrsquot know all the other classes
that extend it
bull Reflection can be used to obtain information about a class its members or its methods
CET230 -- Razdan et al 20
Reflection cont
bull The Class class (see javalang) has methods that enable us to get information about the classndash eg getMethod(String name Class
[] parameterTypes) returns ldquoMethodrdquo
bull The Method class (see javalangreflect) has methods that enable us to get information about the Method and even CALL the methodndash Object invoke(Object obj Object[] args)
CET230 -- Razdan et al 21
ldquoBionicrdquo Nodebull We can modify the Node clone as follows
Node nodeClonetry nodeClone = (Node) superclone() catch( CloneNotSupportedException e ) throw new CloneNotSupportedException()if( thisdata instanceof Cloneable ) try Class c = thisdatagetClass() Method m = cgetMethod( clone null )
nodeClonedata = minvoke( thisdata null ) catch( Exception e ) nodeClonedata = thisdata else nodeClonedata = thisdataif( thisnext = null ) nodeClonenext = (Node) thisnextclone()else nodeClonenext = nullreturn( nodeClone )
CET230 -- Razdan et al 22
Revisiting the String classbull Some useful String methods
ndash charAt( int index)
ndash indexOf( char ch )
ndash indexOf( String str )
ndash split( String regex )
ndash startsWith( String prefix )
ndash substring( int beginIndex int endIndex )
ndash toLowerCase()
ndash toUpperCase()
Note StringTokenizer is a legacy class that is retained for compatibility reasons although its use is discouraged in new code It is recommended that anyone seeking this functionality use the split method of String or the javautilregex package instead
CET230 -- Razdan et al 23
Using Files for IObull Using files for IO is similar to standard IObull For standard input you usually use
ndash InputStreamReaderndash BufferedReader
bull For standard output you usually usendash Systemoutprint or println
bull For file input you can usendash FileReaderndash BufferedReader
bull For file output you can usendash FileWriterndash BufferedWriter
CET230 -- Razdan et al 24
FileReader constructorFileReader
public FileReader(String fileName) throws FileNotFoundException
Creates a new FileReader given the name of the file to read from
Parameters fileName - the name of the file to read from
Throws FileNotFoundException - if the named file does not exist is a directory rather than a regular file or for some other reason cannot be opened for reading
CET230 -- Razdan et al 25
Read ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )
String s = inreadLine()int i = 1while( s = null )
Systemoutprintln(ldquoLine ldquo + i + ldquo ldquo + s )
i++s = inreadLine()
inclose()
CET230 -- Razdan et al 26
FileWriter constructor
FileWriter
public FileWriter(String fileName) throws IOException Constructs a FileWriter object given a file name
Parameters fileName - String The system-dependent filename
Throws IOException - if the named file exists but is a directory rather than a regular file does not exist but cannot be created or cannot be opened for any other reason
CET230 -- Razdan et al 27
BufferedWriter
Method Summary void
close() Close the stream
voidflush() Flush the stream
voidnewLine() Write a line separator
voidwrite(char[] cbuf int off int len) Write a portion of an array of characters
voidwrite(int c) Write a single character
voidwrite(String s int off int len) Write a portion of a String
CET230 -- Razdan et al 28
Write ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )BufferedWriter out = new BufferedWriter(
new FileWriter(outfile) )
String s = inreadLine()while( s = null )
outwrite((ssplit(ldquosrdquo))[0])outnewLine()s = inreadLine()
inclose()outclose()
CET230 -- Razdan et al 29
Java Interfaces
bull A Java interface is a set of related methods that a programmer may want to support in a single classndash Eg Cloneablendash Eg Comparablehttpjavasuncomj2se150docsapijavalangComparablehtml
CET230 -- Razdan et al 30
Iterator Pattern
bull Motivation ndash an aggregate object should give you a way to access its
elements without exposing its internal structure
ndash Use of the object may want to traverse the object in many different ways ndash donrsquot want to bloat the interface with may traversal methods even if you could anticipate all the methods needed
ndash May need to have more than one traversal pending on the aggregate at once
CET230 -- Razdan et al 31
Iterator Patternbull Key idea take responsibility for access and
traversal out of the object and put it into an iterator object
bull Iterator provides basic ldquonavigationrdquo methods eg ndash Firstndash Nextndash IsDonendash CurrentItem
CET230 -- Razdan et al 32
Map Interface
bull A map is a collection class in which keyvalue pairs may be added A pair can be retrieved or removed by specifying just its key
CET230 -- Razdan et al 33
TreeMap
bull Javarsquos TreeMapltK Vgt implements the map interface in an efficient way in which the keys are required to come from a class (such as String) that implements the Comparable interface
CET230 -- Razdan et al 34
Example
bull From package javautil
bull TreeMapltString Integergt frequencyData
bull String word
bull Integer count
CET230 -- Razdan et al 35
Operations
bull public V get(K key)
bull public V put(K key V value)
bull public boolean containsKey(K key)
bull public SetltKgt keySet()
bull public int size()
bull public void clear()
CET230 -- Razdan et al 36
Iteration
for (String word wordMapkeySet())
hellipprocess this key which is in variable wordhellip
CET230 -- Razdan et al 20
Reflection cont
bull The Class class (see javalang) has methods that enable us to get information about the classndash eg getMethod(String name Class
[] parameterTypes) returns ldquoMethodrdquo
bull The Method class (see javalangreflect) has methods that enable us to get information about the Method and even CALL the methodndash Object invoke(Object obj Object[] args)
CET230 -- Razdan et al 21
ldquoBionicrdquo Nodebull We can modify the Node clone as follows
Node nodeClonetry nodeClone = (Node) superclone() catch( CloneNotSupportedException e ) throw new CloneNotSupportedException()if( thisdata instanceof Cloneable ) try Class c = thisdatagetClass() Method m = cgetMethod( clone null )
nodeClonedata = minvoke( thisdata null ) catch( Exception e ) nodeClonedata = thisdata else nodeClonedata = thisdataif( thisnext = null ) nodeClonenext = (Node) thisnextclone()else nodeClonenext = nullreturn( nodeClone )
CET230 -- Razdan et al 22
Revisiting the String classbull Some useful String methods
ndash charAt( int index)
ndash indexOf( char ch )
ndash indexOf( String str )
ndash split( String regex )
ndash startsWith( String prefix )
ndash substring( int beginIndex int endIndex )
ndash toLowerCase()
ndash toUpperCase()
Note StringTokenizer is a legacy class that is retained for compatibility reasons although its use is discouraged in new code It is recommended that anyone seeking this functionality use the split method of String or the javautilregex package instead
CET230 -- Razdan et al 23
Using Files for IObull Using files for IO is similar to standard IObull For standard input you usually use
ndash InputStreamReaderndash BufferedReader
bull For standard output you usually usendash Systemoutprint or println
bull For file input you can usendash FileReaderndash BufferedReader
bull For file output you can usendash FileWriterndash BufferedWriter
CET230 -- Razdan et al 24
FileReader constructorFileReader
public FileReader(String fileName) throws FileNotFoundException
Creates a new FileReader given the name of the file to read from
Parameters fileName - the name of the file to read from
Throws FileNotFoundException - if the named file does not exist is a directory rather than a regular file or for some other reason cannot be opened for reading
CET230 -- Razdan et al 25
Read ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )
String s = inreadLine()int i = 1while( s = null )
Systemoutprintln(ldquoLine ldquo + i + ldquo ldquo + s )
i++s = inreadLine()
inclose()
CET230 -- Razdan et al 26
FileWriter constructor
FileWriter
public FileWriter(String fileName) throws IOException Constructs a FileWriter object given a file name
Parameters fileName - String The system-dependent filename
Throws IOException - if the named file exists but is a directory rather than a regular file does not exist but cannot be created or cannot be opened for any other reason
CET230 -- Razdan et al 27
BufferedWriter
Method Summary void
close() Close the stream
voidflush() Flush the stream
voidnewLine() Write a line separator
voidwrite(char[] cbuf int off int len) Write a portion of an array of characters
voidwrite(int c) Write a single character
voidwrite(String s int off int len) Write a portion of a String
CET230 -- Razdan et al 28
Write ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )BufferedWriter out = new BufferedWriter(
new FileWriter(outfile) )
String s = inreadLine()while( s = null )
outwrite((ssplit(ldquosrdquo))[0])outnewLine()s = inreadLine()
inclose()outclose()
CET230 -- Razdan et al 29
Java Interfaces
bull A Java interface is a set of related methods that a programmer may want to support in a single classndash Eg Cloneablendash Eg Comparablehttpjavasuncomj2se150docsapijavalangComparablehtml
CET230 -- Razdan et al 30
Iterator Pattern
bull Motivation ndash an aggregate object should give you a way to access its
elements without exposing its internal structure
ndash Use of the object may want to traverse the object in many different ways ndash donrsquot want to bloat the interface with may traversal methods even if you could anticipate all the methods needed
ndash May need to have more than one traversal pending on the aggregate at once
CET230 -- Razdan et al 31
Iterator Patternbull Key idea take responsibility for access and
traversal out of the object and put it into an iterator object
bull Iterator provides basic ldquonavigationrdquo methods eg ndash Firstndash Nextndash IsDonendash CurrentItem
CET230 -- Razdan et al 32
Map Interface
bull A map is a collection class in which keyvalue pairs may be added A pair can be retrieved or removed by specifying just its key
CET230 -- Razdan et al 33
TreeMap
bull Javarsquos TreeMapltK Vgt implements the map interface in an efficient way in which the keys are required to come from a class (such as String) that implements the Comparable interface
CET230 -- Razdan et al 34
Example
bull From package javautil
bull TreeMapltString Integergt frequencyData
bull String word
bull Integer count
CET230 -- Razdan et al 35
Operations
bull public V get(K key)
bull public V put(K key V value)
bull public boolean containsKey(K key)
bull public SetltKgt keySet()
bull public int size()
bull public void clear()
CET230 -- Razdan et al 36
Iteration
for (String word wordMapkeySet())
hellipprocess this key which is in variable wordhellip
CET230 -- Razdan et al 21
ldquoBionicrdquo Nodebull We can modify the Node clone as follows
Node nodeClonetry nodeClone = (Node) superclone() catch( CloneNotSupportedException e ) throw new CloneNotSupportedException()if( thisdata instanceof Cloneable ) try Class c = thisdatagetClass() Method m = cgetMethod( clone null )
nodeClonedata = minvoke( thisdata null ) catch( Exception e ) nodeClonedata = thisdata else nodeClonedata = thisdataif( thisnext = null ) nodeClonenext = (Node) thisnextclone()else nodeClonenext = nullreturn( nodeClone )
CET230 -- Razdan et al 22
Revisiting the String classbull Some useful String methods
ndash charAt( int index)
ndash indexOf( char ch )
ndash indexOf( String str )
ndash split( String regex )
ndash startsWith( String prefix )
ndash substring( int beginIndex int endIndex )
ndash toLowerCase()
ndash toUpperCase()
Note StringTokenizer is a legacy class that is retained for compatibility reasons although its use is discouraged in new code It is recommended that anyone seeking this functionality use the split method of String or the javautilregex package instead
CET230 -- Razdan et al 23
Using Files for IObull Using files for IO is similar to standard IObull For standard input you usually use
ndash InputStreamReaderndash BufferedReader
bull For standard output you usually usendash Systemoutprint or println
bull For file input you can usendash FileReaderndash BufferedReader
bull For file output you can usendash FileWriterndash BufferedWriter
CET230 -- Razdan et al 24
FileReader constructorFileReader
public FileReader(String fileName) throws FileNotFoundException
Creates a new FileReader given the name of the file to read from
Parameters fileName - the name of the file to read from
Throws FileNotFoundException - if the named file does not exist is a directory rather than a regular file or for some other reason cannot be opened for reading
CET230 -- Razdan et al 25
Read ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )
String s = inreadLine()int i = 1while( s = null )
Systemoutprintln(ldquoLine ldquo + i + ldquo ldquo + s )
i++s = inreadLine()
inclose()
CET230 -- Razdan et al 26
FileWriter constructor
FileWriter
public FileWriter(String fileName) throws IOException Constructs a FileWriter object given a file name
Parameters fileName - String The system-dependent filename
Throws IOException - if the named file exists but is a directory rather than a regular file does not exist but cannot be created or cannot be opened for any other reason
CET230 -- Razdan et al 27
BufferedWriter
Method Summary void
close() Close the stream
voidflush() Flush the stream
voidnewLine() Write a line separator
voidwrite(char[] cbuf int off int len) Write a portion of an array of characters
voidwrite(int c) Write a single character
voidwrite(String s int off int len) Write a portion of a String
CET230 -- Razdan et al 28
Write ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )BufferedWriter out = new BufferedWriter(
new FileWriter(outfile) )
String s = inreadLine()while( s = null )
outwrite((ssplit(ldquosrdquo))[0])outnewLine()s = inreadLine()
inclose()outclose()
CET230 -- Razdan et al 29
Java Interfaces
bull A Java interface is a set of related methods that a programmer may want to support in a single classndash Eg Cloneablendash Eg Comparablehttpjavasuncomj2se150docsapijavalangComparablehtml
CET230 -- Razdan et al 30
Iterator Pattern
bull Motivation ndash an aggregate object should give you a way to access its
elements without exposing its internal structure
ndash Use of the object may want to traverse the object in many different ways ndash donrsquot want to bloat the interface with may traversal methods even if you could anticipate all the methods needed
ndash May need to have more than one traversal pending on the aggregate at once
CET230 -- Razdan et al 31
Iterator Patternbull Key idea take responsibility for access and
traversal out of the object and put it into an iterator object
bull Iterator provides basic ldquonavigationrdquo methods eg ndash Firstndash Nextndash IsDonendash CurrentItem
CET230 -- Razdan et al 32
Map Interface
bull A map is a collection class in which keyvalue pairs may be added A pair can be retrieved or removed by specifying just its key
CET230 -- Razdan et al 33
TreeMap
bull Javarsquos TreeMapltK Vgt implements the map interface in an efficient way in which the keys are required to come from a class (such as String) that implements the Comparable interface
CET230 -- Razdan et al 34
Example
bull From package javautil
bull TreeMapltString Integergt frequencyData
bull String word
bull Integer count
CET230 -- Razdan et al 35
Operations
bull public V get(K key)
bull public V put(K key V value)
bull public boolean containsKey(K key)
bull public SetltKgt keySet()
bull public int size()
bull public void clear()
CET230 -- Razdan et al 36
Iteration
for (String word wordMapkeySet())
hellipprocess this key which is in variable wordhellip
CET230 -- Razdan et al 22
Revisiting the String classbull Some useful String methods
ndash charAt( int index)
ndash indexOf( char ch )
ndash indexOf( String str )
ndash split( String regex )
ndash startsWith( String prefix )
ndash substring( int beginIndex int endIndex )
ndash toLowerCase()
ndash toUpperCase()
Note StringTokenizer is a legacy class that is retained for compatibility reasons although its use is discouraged in new code It is recommended that anyone seeking this functionality use the split method of String or the javautilregex package instead
CET230 -- Razdan et al 23
Using Files for IObull Using files for IO is similar to standard IObull For standard input you usually use
ndash InputStreamReaderndash BufferedReader
bull For standard output you usually usendash Systemoutprint or println
bull For file input you can usendash FileReaderndash BufferedReader
bull For file output you can usendash FileWriterndash BufferedWriter
CET230 -- Razdan et al 24
FileReader constructorFileReader
public FileReader(String fileName) throws FileNotFoundException
Creates a new FileReader given the name of the file to read from
Parameters fileName - the name of the file to read from
Throws FileNotFoundException - if the named file does not exist is a directory rather than a regular file or for some other reason cannot be opened for reading
CET230 -- Razdan et al 25
Read ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )
String s = inreadLine()int i = 1while( s = null )
Systemoutprintln(ldquoLine ldquo + i + ldquo ldquo + s )
i++s = inreadLine()
inclose()
CET230 -- Razdan et al 26
FileWriter constructor
FileWriter
public FileWriter(String fileName) throws IOException Constructs a FileWriter object given a file name
Parameters fileName - String The system-dependent filename
Throws IOException - if the named file exists but is a directory rather than a regular file does not exist but cannot be created or cannot be opened for any other reason
CET230 -- Razdan et al 27
BufferedWriter
Method Summary void
close() Close the stream
voidflush() Flush the stream
voidnewLine() Write a line separator
voidwrite(char[] cbuf int off int len) Write a portion of an array of characters
voidwrite(int c) Write a single character
voidwrite(String s int off int len) Write a portion of a String
CET230 -- Razdan et al 28
Write ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )BufferedWriter out = new BufferedWriter(
new FileWriter(outfile) )
String s = inreadLine()while( s = null )
outwrite((ssplit(ldquosrdquo))[0])outnewLine()s = inreadLine()
inclose()outclose()
CET230 -- Razdan et al 29
Java Interfaces
bull A Java interface is a set of related methods that a programmer may want to support in a single classndash Eg Cloneablendash Eg Comparablehttpjavasuncomj2se150docsapijavalangComparablehtml
CET230 -- Razdan et al 30
Iterator Pattern
bull Motivation ndash an aggregate object should give you a way to access its
elements without exposing its internal structure
ndash Use of the object may want to traverse the object in many different ways ndash donrsquot want to bloat the interface with may traversal methods even if you could anticipate all the methods needed
ndash May need to have more than one traversal pending on the aggregate at once
CET230 -- Razdan et al 31
Iterator Patternbull Key idea take responsibility for access and
traversal out of the object and put it into an iterator object
bull Iterator provides basic ldquonavigationrdquo methods eg ndash Firstndash Nextndash IsDonendash CurrentItem
CET230 -- Razdan et al 32
Map Interface
bull A map is a collection class in which keyvalue pairs may be added A pair can be retrieved or removed by specifying just its key
CET230 -- Razdan et al 33
TreeMap
bull Javarsquos TreeMapltK Vgt implements the map interface in an efficient way in which the keys are required to come from a class (such as String) that implements the Comparable interface
CET230 -- Razdan et al 34
Example
bull From package javautil
bull TreeMapltString Integergt frequencyData
bull String word
bull Integer count
CET230 -- Razdan et al 35
Operations
bull public V get(K key)
bull public V put(K key V value)
bull public boolean containsKey(K key)
bull public SetltKgt keySet()
bull public int size()
bull public void clear()
CET230 -- Razdan et al 36
Iteration
for (String word wordMapkeySet())
hellipprocess this key which is in variable wordhellip
CET230 -- Razdan et al 23
Using Files for IObull Using files for IO is similar to standard IObull For standard input you usually use
ndash InputStreamReaderndash BufferedReader
bull For standard output you usually usendash Systemoutprint or println
bull For file input you can usendash FileReaderndash BufferedReader
bull For file output you can usendash FileWriterndash BufferedWriter
CET230 -- Razdan et al 24
FileReader constructorFileReader
public FileReader(String fileName) throws FileNotFoundException
Creates a new FileReader given the name of the file to read from
Parameters fileName - the name of the file to read from
Throws FileNotFoundException - if the named file does not exist is a directory rather than a regular file or for some other reason cannot be opened for reading
CET230 -- Razdan et al 25
Read ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )
String s = inreadLine()int i = 1while( s = null )
Systemoutprintln(ldquoLine ldquo + i + ldquo ldquo + s )
i++s = inreadLine()
inclose()
CET230 -- Razdan et al 26
FileWriter constructor
FileWriter
public FileWriter(String fileName) throws IOException Constructs a FileWriter object given a file name
Parameters fileName - String The system-dependent filename
Throws IOException - if the named file exists but is a directory rather than a regular file does not exist but cannot be created or cannot be opened for any other reason
CET230 -- Razdan et al 27
BufferedWriter
Method Summary void
close() Close the stream
voidflush() Flush the stream
voidnewLine() Write a line separator
voidwrite(char[] cbuf int off int len) Write a portion of an array of characters
voidwrite(int c) Write a single character
voidwrite(String s int off int len) Write a portion of a String
CET230 -- Razdan et al 28
Write ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )BufferedWriter out = new BufferedWriter(
new FileWriter(outfile) )
String s = inreadLine()while( s = null )
outwrite((ssplit(ldquosrdquo))[0])outnewLine()s = inreadLine()
inclose()outclose()
CET230 -- Razdan et al 29
Java Interfaces
bull A Java interface is a set of related methods that a programmer may want to support in a single classndash Eg Cloneablendash Eg Comparablehttpjavasuncomj2se150docsapijavalangComparablehtml
CET230 -- Razdan et al 30
Iterator Pattern
bull Motivation ndash an aggregate object should give you a way to access its
elements without exposing its internal structure
ndash Use of the object may want to traverse the object in many different ways ndash donrsquot want to bloat the interface with may traversal methods even if you could anticipate all the methods needed
ndash May need to have more than one traversal pending on the aggregate at once
CET230 -- Razdan et al 31
Iterator Patternbull Key idea take responsibility for access and
traversal out of the object and put it into an iterator object
bull Iterator provides basic ldquonavigationrdquo methods eg ndash Firstndash Nextndash IsDonendash CurrentItem
CET230 -- Razdan et al 32
Map Interface
bull A map is a collection class in which keyvalue pairs may be added A pair can be retrieved or removed by specifying just its key
CET230 -- Razdan et al 33
TreeMap
bull Javarsquos TreeMapltK Vgt implements the map interface in an efficient way in which the keys are required to come from a class (such as String) that implements the Comparable interface
CET230 -- Razdan et al 34
Example
bull From package javautil
bull TreeMapltString Integergt frequencyData
bull String word
bull Integer count
CET230 -- Razdan et al 35
Operations
bull public V get(K key)
bull public V put(K key V value)
bull public boolean containsKey(K key)
bull public SetltKgt keySet()
bull public int size()
bull public void clear()
CET230 -- Razdan et al 36
Iteration
for (String word wordMapkeySet())
hellipprocess this key which is in variable wordhellip
CET230 -- Razdan et al 24
FileReader constructorFileReader
public FileReader(String fileName) throws FileNotFoundException
Creates a new FileReader given the name of the file to read from
Parameters fileName - the name of the file to read from
Throws FileNotFoundException - if the named file does not exist is a directory rather than a regular file or for some other reason cannot be opened for reading
CET230 -- Razdan et al 25
Read ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )
String s = inreadLine()int i = 1while( s = null )
Systemoutprintln(ldquoLine ldquo + i + ldquo ldquo + s )
i++s = inreadLine()
inclose()
CET230 -- Razdan et al 26
FileWriter constructor
FileWriter
public FileWriter(String fileName) throws IOException Constructs a FileWriter object given a file name
Parameters fileName - String The system-dependent filename
Throws IOException - if the named file exists but is a directory rather than a regular file does not exist but cannot be created or cannot be opened for any other reason
CET230 -- Razdan et al 27
BufferedWriter
Method Summary void
close() Close the stream
voidflush() Flush the stream
voidnewLine() Write a line separator
voidwrite(char[] cbuf int off int len) Write a portion of an array of characters
voidwrite(int c) Write a single character
voidwrite(String s int off int len) Write a portion of a String
CET230 -- Razdan et al 28
Write ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )BufferedWriter out = new BufferedWriter(
new FileWriter(outfile) )
String s = inreadLine()while( s = null )
outwrite((ssplit(ldquosrdquo))[0])outnewLine()s = inreadLine()
inclose()outclose()
CET230 -- Razdan et al 29
Java Interfaces
bull A Java interface is a set of related methods that a programmer may want to support in a single classndash Eg Cloneablendash Eg Comparablehttpjavasuncomj2se150docsapijavalangComparablehtml
CET230 -- Razdan et al 30
Iterator Pattern
bull Motivation ndash an aggregate object should give you a way to access its
elements without exposing its internal structure
ndash Use of the object may want to traverse the object in many different ways ndash donrsquot want to bloat the interface with may traversal methods even if you could anticipate all the methods needed
ndash May need to have more than one traversal pending on the aggregate at once
CET230 -- Razdan et al 31
Iterator Patternbull Key idea take responsibility for access and
traversal out of the object and put it into an iterator object
bull Iterator provides basic ldquonavigationrdquo methods eg ndash Firstndash Nextndash IsDonendash CurrentItem
CET230 -- Razdan et al 32
Map Interface
bull A map is a collection class in which keyvalue pairs may be added A pair can be retrieved or removed by specifying just its key
CET230 -- Razdan et al 33
TreeMap
bull Javarsquos TreeMapltK Vgt implements the map interface in an efficient way in which the keys are required to come from a class (such as String) that implements the Comparable interface
CET230 -- Razdan et al 34
Example
bull From package javautil
bull TreeMapltString Integergt frequencyData
bull String word
bull Integer count
CET230 -- Razdan et al 35
Operations
bull public V get(K key)
bull public V put(K key V value)
bull public boolean containsKey(K key)
bull public SetltKgt keySet()
bull public int size()
bull public void clear()
CET230 -- Razdan et al 36
Iteration
for (String word wordMapkeySet())
hellipprocess this key which is in variable wordhellip
CET230 -- Razdan et al 25
Read ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )
String s = inreadLine()int i = 1while( s = null )
Systemoutprintln(ldquoLine ldquo + i + ldquo ldquo + s )
i++s = inreadLine()
inclose()
CET230 -- Razdan et al 26
FileWriter constructor
FileWriter
public FileWriter(String fileName) throws IOException Constructs a FileWriter object given a file name
Parameters fileName - String The system-dependent filename
Throws IOException - if the named file exists but is a directory rather than a regular file does not exist but cannot be created or cannot be opened for any other reason
CET230 -- Razdan et al 27
BufferedWriter
Method Summary void
close() Close the stream
voidflush() Flush the stream
voidnewLine() Write a line separator
voidwrite(char[] cbuf int off int len) Write a portion of an array of characters
voidwrite(int c) Write a single character
voidwrite(String s int off int len) Write a portion of a String
CET230 -- Razdan et al 28
Write ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )BufferedWriter out = new BufferedWriter(
new FileWriter(outfile) )
String s = inreadLine()while( s = null )
outwrite((ssplit(ldquosrdquo))[0])outnewLine()s = inreadLine()
inclose()outclose()
CET230 -- Razdan et al 29
Java Interfaces
bull A Java interface is a set of related methods that a programmer may want to support in a single classndash Eg Cloneablendash Eg Comparablehttpjavasuncomj2se150docsapijavalangComparablehtml
CET230 -- Razdan et al 30
Iterator Pattern
bull Motivation ndash an aggregate object should give you a way to access its
elements without exposing its internal structure
ndash Use of the object may want to traverse the object in many different ways ndash donrsquot want to bloat the interface with may traversal methods even if you could anticipate all the methods needed
ndash May need to have more than one traversal pending on the aggregate at once
CET230 -- Razdan et al 31
Iterator Patternbull Key idea take responsibility for access and
traversal out of the object and put it into an iterator object
bull Iterator provides basic ldquonavigationrdquo methods eg ndash Firstndash Nextndash IsDonendash CurrentItem
CET230 -- Razdan et al 32
Map Interface
bull A map is a collection class in which keyvalue pairs may be added A pair can be retrieved or removed by specifying just its key
CET230 -- Razdan et al 33
TreeMap
bull Javarsquos TreeMapltK Vgt implements the map interface in an efficient way in which the keys are required to come from a class (such as String) that implements the Comparable interface
CET230 -- Razdan et al 34
Example
bull From package javautil
bull TreeMapltString Integergt frequencyData
bull String word
bull Integer count
CET230 -- Razdan et al 35
Operations
bull public V get(K key)
bull public V put(K key V value)
bull public boolean containsKey(K key)
bull public SetltKgt keySet()
bull public int size()
bull public void clear()
CET230 -- Razdan et al 36
Iteration
for (String word wordMapkeySet())
hellipprocess this key which is in variable wordhellip
CET230 -- Razdan et al 26
FileWriter constructor
FileWriter
public FileWriter(String fileName) throws IOException Constructs a FileWriter object given a file name
Parameters fileName - String The system-dependent filename
Throws IOException - if the named file exists but is a directory rather than a regular file does not exist but cannot be created or cannot be opened for any other reason
CET230 -- Razdan et al 27
BufferedWriter
Method Summary void
close() Close the stream
voidflush() Flush the stream
voidnewLine() Write a line separator
voidwrite(char[] cbuf int off int len) Write a portion of an array of characters
voidwrite(int c) Write a single character
voidwrite(String s int off int len) Write a portion of a String
CET230 -- Razdan et al 28
Write ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )BufferedWriter out = new BufferedWriter(
new FileWriter(outfile) )
String s = inreadLine()while( s = null )
outwrite((ssplit(ldquosrdquo))[0])outnewLine()s = inreadLine()
inclose()outclose()
CET230 -- Razdan et al 29
Java Interfaces
bull A Java interface is a set of related methods that a programmer may want to support in a single classndash Eg Cloneablendash Eg Comparablehttpjavasuncomj2se150docsapijavalangComparablehtml
CET230 -- Razdan et al 30
Iterator Pattern
bull Motivation ndash an aggregate object should give you a way to access its
elements without exposing its internal structure
ndash Use of the object may want to traverse the object in many different ways ndash donrsquot want to bloat the interface with may traversal methods even if you could anticipate all the methods needed
ndash May need to have more than one traversal pending on the aggregate at once
CET230 -- Razdan et al 31
Iterator Patternbull Key idea take responsibility for access and
traversal out of the object and put it into an iterator object
bull Iterator provides basic ldquonavigationrdquo methods eg ndash Firstndash Nextndash IsDonendash CurrentItem
CET230 -- Razdan et al 32
Map Interface
bull A map is a collection class in which keyvalue pairs may be added A pair can be retrieved or removed by specifying just its key
CET230 -- Razdan et al 33
TreeMap
bull Javarsquos TreeMapltK Vgt implements the map interface in an efficient way in which the keys are required to come from a class (such as String) that implements the Comparable interface
CET230 -- Razdan et al 34
Example
bull From package javautil
bull TreeMapltString Integergt frequencyData
bull String word
bull Integer count
CET230 -- Razdan et al 35
Operations
bull public V get(K key)
bull public V put(K key V value)
bull public boolean containsKey(K key)
bull public SetltKgt keySet()
bull public int size()
bull public void clear()
CET230 -- Razdan et al 36
Iteration
for (String word wordMapkeySet())
hellipprocess this key which is in variable wordhellip
CET230 -- Razdan et al 27
BufferedWriter
Method Summary void
close() Close the stream
voidflush() Flush the stream
voidnewLine() Write a line separator
voidwrite(char[] cbuf int off int len) Write a portion of an array of characters
voidwrite(int c) Write a single character
voidwrite(String s int off int len) Write a portion of a String
CET230 -- Razdan et al 28
Write ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )BufferedWriter out = new BufferedWriter(
new FileWriter(outfile) )
String s = inreadLine()while( s = null )
outwrite((ssplit(ldquosrdquo))[0])outnewLine()s = inreadLine()
inclose()outclose()
CET230 -- Razdan et al 29
Java Interfaces
bull A Java interface is a set of related methods that a programmer may want to support in a single classndash Eg Cloneablendash Eg Comparablehttpjavasuncomj2se150docsapijavalangComparablehtml
CET230 -- Razdan et al 30
Iterator Pattern
bull Motivation ndash an aggregate object should give you a way to access its
elements without exposing its internal structure
ndash Use of the object may want to traverse the object in many different ways ndash donrsquot want to bloat the interface with may traversal methods even if you could anticipate all the methods needed
ndash May need to have more than one traversal pending on the aggregate at once
CET230 -- Razdan et al 31
Iterator Patternbull Key idea take responsibility for access and
traversal out of the object and put it into an iterator object
bull Iterator provides basic ldquonavigationrdquo methods eg ndash Firstndash Nextndash IsDonendash CurrentItem
CET230 -- Razdan et al 32
Map Interface
bull A map is a collection class in which keyvalue pairs may be added A pair can be retrieved or removed by specifying just its key
CET230 -- Razdan et al 33
TreeMap
bull Javarsquos TreeMapltK Vgt implements the map interface in an efficient way in which the keys are required to come from a class (such as String) that implements the Comparable interface
CET230 -- Razdan et al 34
Example
bull From package javautil
bull TreeMapltString Integergt frequencyData
bull String word
bull Integer count
CET230 -- Razdan et al 35
Operations
bull public V get(K key)
bull public V put(K key V value)
bull public boolean containsKey(K key)
bull public SetltKgt keySet()
bull public int size()
bull public void clear()
CET230 -- Razdan et al 36
Iteration
for (String word wordMapkeySet())
hellipprocess this key which is in variable wordhellip
CET230 -- Razdan et al 28
Write ExampleBufferedReader in = new BufferedReader(
new FileReader(infile) )BufferedWriter out = new BufferedWriter(
new FileWriter(outfile) )
String s = inreadLine()while( s = null )
outwrite((ssplit(ldquosrdquo))[0])outnewLine()s = inreadLine()
inclose()outclose()
CET230 -- Razdan et al 29
Java Interfaces
bull A Java interface is a set of related methods that a programmer may want to support in a single classndash Eg Cloneablendash Eg Comparablehttpjavasuncomj2se150docsapijavalangComparablehtml
CET230 -- Razdan et al 30
Iterator Pattern
bull Motivation ndash an aggregate object should give you a way to access its
elements without exposing its internal structure
ndash Use of the object may want to traverse the object in many different ways ndash donrsquot want to bloat the interface with may traversal methods even if you could anticipate all the methods needed
ndash May need to have more than one traversal pending on the aggregate at once
CET230 -- Razdan et al 31
Iterator Patternbull Key idea take responsibility for access and
traversal out of the object and put it into an iterator object
bull Iterator provides basic ldquonavigationrdquo methods eg ndash Firstndash Nextndash IsDonendash CurrentItem
CET230 -- Razdan et al 32
Map Interface
bull A map is a collection class in which keyvalue pairs may be added A pair can be retrieved or removed by specifying just its key
CET230 -- Razdan et al 33
TreeMap
bull Javarsquos TreeMapltK Vgt implements the map interface in an efficient way in which the keys are required to come from a class (such as String) that implements the Comparable interface
CET230 -- Razdan et al 34
Example
bull From package javautil
bull TreeMapltString Integergt frequencyData
bull String word
bull Integer count
CET230 -- Razdan et al 35
Operations
bull public V get(K key)
bull public V put(K key V value)
bull public boolean containsKey(K key)
bull public SetltKgt keySet()
bull public int size()
bull public void clear()
CET230 -- Razdan et al 36
Iteration
for (String word wordMapkeySet())
hellipprocess this key which is in variable wordhellip
CET230 -- Razdan et al 29
Java Interfaces
bull A Java interface is a set of related methods that a programmer may want to support in a single classndash Eg Cloneablendash Eg Comparablehttpjavasuncomj2se150docsapijavalangComparablehtml
CET230 -- Razdan et al 30
Iterator Pattern
bull Motivation ndash an aggregate object should give you a way to access its
elements without exposing its internal structure
ndash Use of the object may want to traverse the object in many different ways ndash donrsquot want to bloat the interface with may traversal methods even if you could anticipate all the methods needed
ndash May need to have more than one traversal pending on the aggregate at once
CET230 -- Razdan et al 31
Iterator Patternbull Key idea take responsibility for access and
traversal out of the object and put it into an iterator object
bull Iterator provides basic ldquonavigationrdquo methods eg ndash Firstndash Nextndash IsDonendash CurrentItem
CET230 -- Razdan et al 32
Map Interface
bull A map is a collection class in which keyvalue pairs may be added A pair can be retrieved or removed by specifying just its key
CET230 -- Razdan et al 33
TreeMap
bull Javarsquos TreeMapltK Vgt implements the map interface in an efficient way in which the keys are required to come from a class (such as String) that implements the Comparable interface
CET230 -- Razdan et al 34
Example
bull From package javautil
bull TreeMapltString Integergt frequencyData
bull String word
bull Integer count
CET230 -- Razdan et al 35
Operations
bull public V get(K key)
bull public V put(K key V value)
bull public boolean containsKey(K key)
bull public SetltKgt keySet()
bull public int size()
bull public void clear()
CET230 -- Razdan et al 36
Iteration
for (String word wordMapkeySet())
hellipprocess this key which is in variable wordhellip
CET230 -- Razdan et al 30
Iterator Pattern
bull Motivation ndash an aggregate object should give you a way to access its
elements without exposing its internal structure
ndash Use of the object may want to traverse the object in many different ways ndash donrsquot want to bloat the interface with may traversal methods even if you could anticipate all the methods needed
ndash May need to have more than one traversal pending on the aggregate at once
CET230 -- Razdan et al 31
Iterator Patternbull Key idea take responsibility for access and
traversal out of the object and put it into an iterator object
bull Iterator provides basic ldquonavigationrdquo methods eg ndash Firstndash Nextndash IsDonendash CurrentItem
CET230 -- Razdan et al 32
Map Interface
bull A map is a collection class in which keyvalue pairs may be added A pair can be retrieved or removed by specifying just its key
CET230 -- Razdan et al 33
TreeMap
bull Javarsquos TreeMapltK Vgt implements the map interface in an efficient way in which the keys are required to come from a class (such as String) that implements the Comparable interface
CET230 -- Razdan et al 34
Example
bull From package javautil
bull TreeMapltString Integergt frequencyData
bull String word
bull Integer count
CET230 -- Razdan et al 35
Operations
bull public V get(K key)
bull public V put(K key V value)
bull public boolean containsKey(K key)
bull public SetltKgt keySet()
bull public int size()
bull public void clear()
CET230 -- Razdan et al 36
Iteration
for (String word wordMapkeySet())
hellipprocess this key which is in variable wordhellip
CET230 -- Razdan et al 31
Iterator Patternbull Key idea take responsibility for access and
traversal out of the object and put it into an iterator object
bull Iterator provides basic ldquonavigationrdquo methods eg ndash Firstndash Nextndash IsDonendash CurrentItem
CET230 -- Razdan et al 32
Map Interface
bull A map is a collection class in which keyvalue pairs may be added A pair can be retrieved or removed by specifying just its key
CET230 -- Razdan et al 33
TreeMap
bull Javarsquos TreeMapltK Vgt implements the map interface in an efficient way in which the keys are required to come from a class (such as String) that implements the Comparable interface
CET230 -- Razdan et al 34
Example
bull From package javautil
bull TreeMapltString Integergt frequencyData
bull String word
bull Integer count
CET230 -- Razdan et al 35
Operations
bull public V get(K key)
bull public V put(K key V value)
bull public boolean containsKey(K key)
bull public SetltKgt keySet()
bull public int size()
bull public void clear()
CET230 -- Razdan et al 36
Iteration
for (String word wordMapkeySet())
hellipprocess this key which is in variable wordhellip
CET230 -- Razdan et al 32
Map Interface
bull A map is a collection class in which keyvalue pairs may be added A pair can be retrieved or removed by specifying just its key
CET230 -- Razdan et al 33
TreeMap
bull Javarsquos TreeMapltK Vgt implements the map interface in an efficient way in which the keys are required to come from a class (such as String) that implements the Comparable interface
CET230 -- Razdan et al 34
Example
bull From package javautil
bull TreeMapltString Integergt frequencyData
bull String word
bull Integer count
CET230 -- Razdan et al 35
Operations
bull public V get(K key)
bull public V put(K key V value)
bull public boolean containsKey(K key)
bull public SetltKgt keySet()
bull public int size()
bull public void clear()
CET230 -- Razdan et al 36
Iteration
for (String word wordMapkeySet())
hellipprocess this key which is in variable wordhellip
CET230 -- Razdan et al 33
TreeMap
bull Javarsquos TreeMapltK Vgt implements the map interface in an efficient way in which the keys are required to come from a class (such as String) that implements the Comparable interface
CET230 -- Razdan et al 34
Example
bull From package javautil
bull TreeMapltString Integergt frequencyData
bull String word
bull Integer count
CET230 -- Razdan et al 35
Operations
bull public V get(K key)
bull public V put(K key V value)
bull public boolean containsKey(K key)
bull public SetltKgt keySet()
bull public int size()
bull public void clear()
CET230 -- Razdan et al 36
Iteration
for (String word wordMapkeySet())
hellipprocess this key which is in variable wordhellip
CET230 -- Razdan et al 34
Example
bull From package javautil
bull TreeMapltString Integergt frequencyData
bull String word
bull Integer count
CET230 -- Razdan et al 35
Operations
bull public V get(K key)
bull public V put(K key V value)
bull public boolean containsKey(K key)
bull public SetltKgt keySet()
bull public int size()
bull public void clear()
CET230 -- Razdan et al 36
Iteration
for (String word wordMapkeySet())
hellipprocess this key which is in variable wordhellip
CET230 -- Razdan et al 35
Operations
bull public V get(K key)
bull public V put(K key V value)
bull public boolean containsKey(K key)
bull public SetltKgt keySet()
bull public int size()
bull public void clear()
CET230 -- Razdan et al 36
Iteration
for (String word wordMapkeySet())
hellipprocess this key which is in variable wordhellip
CET230 -- Razdan et al 36
Iteration
for (String word wordMapkeySet())
hellipprocess this key which is in variable wordhellip
![Pt1286633[Anshuman Arya] Final Pptmaking of Piston](https://img.dokumen.tips/doc/110x75/563dbab7550346aa9aa776ea/pt1286633anshuman-arya-final-pptmaking-of-piston.jpg)
