Shlomo Hershkop 2007 1 Advanced Review. Shlomo Hershkop 20072 Advanced Review Time classes Time classes Date Classes Date Classes File input/output File

Shlomo Hershkop 2007Shlomo Hershkop 2007 11

Advanced ReviewAdvanced Review


Advanced ReviewAdvanced Review

Time classesTime classes Date ClassesDate Classes File input/output File input/output PackagesPackages


Multiple dimensionsMultiple dimensions

No reason cant create 4,5,6 No reason cant create 4,5,6 dimension arraysdimension arrays

Gets hard to manageGets hard to manage Better idea: Better idea:

Think about another way of representing Think about another way of representing the datathe data

Often creating an object is a better Often creating an object is a better approachapproach


Arrays furtherArrays further

Need to explicitly copy contents of arrays when Need to explicitly copy contents of arrays when resizing arrays with temp oneresizing arrays with temp one

Better solution:Better solution: ArrayListArrayList VectorVector

Full object versions of arraysFull object versions of arrays Capacity can grow over timeCapacity can grow over time Useful methods bundles with themUseful methods bundles with them


codecode

Create a new class with a main called VectorTestCreate a new class with a main called VectorTest

Create a vectorCreate a vector

Put in some stuffPut in some stuff Print them outPrint them out Replace something in the middleReplace something in the middle Print it outPrint it out Clear the vectorClear the vector Print it outPrint it out


Default valuesDefault values

Should be aware if you forget to set Should be aware if you forget to set valuesvalues

Might mess up your logicMight mess up your logic Think of multiplying a bunch of numbers Think of multiplying a bunch of numbers

and not setting one of them…and not setting one of them… Compiler/IDE will let you know if you Compiler/IDE will let you know if you

forgot to set values (warning)forgot to set values (warning)


TimeTime

Next lets discuss how time is handled Next lets discuss how time is handled in Javain Java

Java.util.Date is the way java Java.util.Date is the way java represents a point in timerepresents a point in time

It is measured in millisecondsIt is measured in milliseconds Time = 0 what does that mean?Time = 0 what does that mean?


DateDate

Time 0 = first millisecond in 1970Time 0 = first millisecond in 1970 Historical reasons for thisHistorical reasons for this

long is the type it useslong is the type it uses Range to +9,223,372,036,854,775,807Range to +9,223,372,036,854,775,807 Don’t memorize thatDon’t memorize that

Lets look at the APILets look at the API What is a deprecated method ??What is a deprecated method ??

Example: getDay() ??Example: getDay() ??


Why DateWhy Date

Why are we wrapping the time long Why are we wrapping the time long number?number?

"I'll see you on 996,321,998,346." doesn’t "I'll see you on 996,321,998,346." doesn’t really workreally work

Also allows you to easily order and compare Also allows you to easily order and compare different points in time….meaningfullydifferent points in time….meaningfully


Change over time (no pun)Change over time (no pun)

Nothing you program should be set in stoneNothing you program should be set in stone

Sometimes your design changesSometimes your design changes

Need to go back and change your codeNeed to go back and change your code

Deprecated methods are those which have Deprecated methods are those which have been replaced…but left in place so your old been replaced…but left in place so your old stuff shouldn’t crash if you try to recompile stuff shouldn’t crash if you try to recompile with latest jdkwith latest jdk


Back to timeBack to time

System.currentTimeMillis()System.currentTimeMillis() Returns the current time on the systemReturns the current time on the system As a Date ObjectAs a Date Object


Ideas Ideas

Although would like to represent a Although would like to represent a point in time, usually time is point in time, usually time is associated with other measurementsassociated with other measurements

MonthMonth YearYear


The GregorianCalendar The GregorianCalendar ClassClass

The Date class doesn't measure The Date class doesn't measure months, weekdays, etc.months, weekdays, etc.

That's the job of a calendarThat's the job of a calendar A calendar assigns a name to a point A calendar assigns a name to a point

in timein time Many calendars in use:Many calendars in use:

GregorianGregorian Contemporary: Hebrew, Arabic, ChineseContemporary: Hebrew, Arabic, Chinese Historical: French Revolutionary, MayanHistorical: French Revolutionary, Mayan


RelationshipsRelationships


Next stepNext step

Lets design a new class to represent a Lets design a new class to represent a dayday

Today is TuesdayToday is TuesdayDay today = new Day();Day today = new Day();

Today.add(1);Today.add(1); //should give us Wednesday //should give us Wednesday


Goal of Day ClassGoal of Day Class

Answer questions such asAnswer questions such as

How many days are there between How many days are there between now and the end of the year?now and the end of the year?

What day is 100 days from now?What day is 100 days from now? How many days till my birthday (I’ve How many days till my birthday (I’ve

always wanted a _____________)always wanted a _____________)


Designing the classDesigning the class

Lets have a method Lets have a method daysFrom it computes number of days between two days:daysFrom it computes number of days between two days:

int n = today.daysFrom(birthday);int n = today.daysFrom(birthday);

addDays computes a day that is some days away from a addDays computes a day that is some days away from a given day:given day:

Day later = today.addDays(999);Day later = today.addDays(999);

Mathematical relationship:Mathematical relationship:

d.addDays(n).daysFrom(d) == nd.addDays(n).daysFrom(d) == nd1.addDays(d2.daysFrom(d1)) == d2d1.addDays(d2.daysFrom(d1)) == d2


Constructor Date(int year, int month, Constructor Date(int year, int month, int date)int date)

Will need the following methods:Will need the following methods: getYeargetYear getMonthgetMonth getDategetDate


ImplementationImplementation

Straightforward which member will need:Straightforward which member will need:

private int yearprivate int yearprivate int monthprivate int monthprivate int dateprivate int date

addDays/daysBetween tedious to implementaddDays/daysBetween tedious to implement April, June, September, November have 30 daysApril, June, September, November have 30 days February has 28 days, except in leap years it has 29 daysFebruary has 28 days, except in leap years it has 29 days All other months have 31 daysAll other months have 31 days Leap years are divisible by 4, except after 1582, years divisible Leap years are divisible by 4, except after 1582, years divisible

by 100 but not 400 are not leap yearsby 100 but not 400 are not leap years There is no year 0; year 1 is preceded by year -1There is no year 0; year 1 is preceded by year -1 In the switchover to the Gregorian calendar, ten days were In the switchover to the Gregorian calendar, ten days were

dropped: October 15, 1582 is preceded by October 4dropped: October 15, 1582 is preceded by October 4


Day CodeDay Code

public Day(int aYear, int aMonth, int aDate)public Day(int aYear, int aMonth, int aDate){{

year = aYear;year = aYear;month = aMonth;month = aMonth;date = aDate;date = aDate;

}}

private int year;private int year;private int month;private int month;private int date;private int date;

private static final int[] DAYS_PER_MONTH private static final int[] DAYS_PER_MONTH = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };= { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };

private static final int GREGORIAN_START_YEAR = 1582;private static final int GREGORIAN_START_YEAR = 1582;private static final int GREGORIAN_START_MONTH = 10;private static final int GREGORIAN_START_MONTH = 10;private static final int GREGORIAN_START_DAY = 15;private static final int GREGORIAN_START_DAY = 15;private static final int JULIAN_END_DAY = 4;private static final int JULIAN_END_DAY = 4;

private static final int JANUARY = 1;private static final int JANUARY = 1;private static final int FEBRUARY = 2;private static final int FEBRUARY = 2;private static final int DECEMBER = 12;private static final int DECEMBER = 12;


Day CodeDay Code

private Day nextDay()private Day nextDay()112: {112: {113: int y = year;113: int y = year;114: int m = month;114: int m = month;115: int d = date;115: int d = date;116: 116: 117: if (y == GREGORIAN_START_YEAR117: if (y == GREGORIAN_START_YEAR118: && m == GREGORIAN_START_MONTH118: && m == GREGORIAN_START_MONTH119: && d == JULIAN_END_DAY)119: && d == JULIAN_END_DAY)120: d = GREGORIAN_START_DAY;120: d = GREGORIAN_START_DAY;121: else if (d < daysPerMonth(y, m))121: else if (d < daysPerMonth(y, m))122: d++;122: d++;123: else123: else124: {124: {125: d = 1;125: d = 1;126: m++;126: m++;127: if (m > DECEMBER) 127: if (m > DECEMBER) 128: { 128: { 129: m = JANUARY; 129: m = JANUARY; 130: y++; 130: y++; 131: if (y == 0) y++;131: if (y == 0) y++;132: }132: }133: }133: }134: return new Day(y, m, d);134: return new Day(y, m, d);135: }135: }


private static int daysPerMonth(int y, int m)private static int daysPerMonth(int y, int m){{

int days = DAYS_PER_MONTH[m - 1];int days = DAYS_PER_MONTH[m - 1]; if (m == FEBRUARY && isLeapYear(y)) if (m == FEBRUARY && isLeapYear(y)) days++;days++; return days;return days;

}}

private static boolean isLeapYear(int y)private static boolean isLeapYear(int y){{if (y % 4 != 0) return false;if (y % 4 != 0) return false;if (y < GREGORIAN_START_YEAR) return true;if (y < GREGORIAN_START_YEAR) return true;return (y % 100 != 0) || (y % 400 == 0);return (y % 100 != 0) || (y % 400 == 0);}}


TesterTester

01: public class DayTester01: public class DayTester02: {02: {03: public static void main(String[] args)03: public static void main(String[] args)04: {04: {05: Day today = new Day(2001, 2, 3);05: Day today = new Day(2001, 2, 3);

//February 3, 2001//February 3, 200106: Day later = today.addDays(999);06: Day later = today.addDays(999);07: System.out.println(later.getYear() 07: System.out.println(later.getYear() 08: + "-" + later.getMonth() 08: + "-" + later.getMonth() 09: + "-" + later.getDate()); 09: + "-" + later.getDate()); 10: System.out.println(later.daysFrom(today));10: System.out.println(later.daysFrom(today));

// Prints 999// Prints 99911: }11: }12: }12: }


Notice Notice

Private helper methodsPrivate helper methods

Notice all the work to increment a Notice all the work to increment a dayday


Another ideaAnother idea

This is for illustration, don’t need to codeThis is for illustration, don’t need to code

For greater efficiency, we can use Julian For greater efficiency, we can use Julian day numberday number

Used in astronomyUsed in astronomy Number of days since Jan. 1, 4713 BCENumber of days since Jan. 1, 4713 BCE May 23, 1968 = Julian Day 2,440,000May 23, 1968 = Julian Day 2,440,000 Greatly simplifies date arithmeticGreatly simplifies date arithmetic


CodeCode

public Day(int aYear, int aMonth, int aDate)public Day(int aYear, int aMonth, int aDate)

{{

//notice we are calling a private//notice we are calling a private

//helper function//helper function

julian = toJulian(aYear, aMonth, aDate);julian = toJulian(aYear, aMonth, aDate);

}}

//that’s all we need//that’s all we need

private int julian;private int julian;


Helper functionHelper function

private static int toJulian(int year, int month, int date)private static int toJulian(int year, int month, int date){ {

int jy = year;int jy = year;if (year < 0) jy++;if (year < 0) jy++;int jm = month;int jm = month;if (month > 2) jm++;if (month > 2) jm++;else{ else{

jy--;jy--;jm += 13;jm += 13;

}}int jul = (int) (java.lang.Math.floor(365.25 * jy) int jul = (int) (java.lang.Math.floor(365.25 * jy) + java.lang.Math.floor(30.6001 * jm) + date + 1720995.0);+ java.lang.Math.floor(30.6001 * jm) + date + 1720995.0);int IGREG = 15 + 31 * (10 + 12 * 1582);int IGREG = 15 + 31 * (10 + 12 * 1582);

// Gregorian Calendar adopted Oct. 15, 1582// Gregorian Calendar adopted Oct. 15, 1582if (date + 31 * (month + 12 * year) >= IGREG)if (date + 31 * (month + 12 * year) >= IGREG)// Change over to Gregorian calendar// Change over to Gregorian calendar{ { int ja = (int) (0.01 * jy);int ja = (int) (0.01 * jy);jul += 2 - ja + (int) (0.25 * ja);jul += 2 - ja + (int) (0.25 * ja);}}return jul;return jul;

}}


Any other ideas?Any other ideas?

So you see that using the class doesn’t So you see that using the class doesn’t change even though we totally changed change even though we totally changed how the inside workshow the inside works Called encapsulationCalled encapsulation

So its easy to move up or down the So its easy to move up or down the calendarcalendar Add subtractAdd subtract

Where would it cost us ??Where would it cost us ??


Switch gearsSwitch gears

Lets talk about how to use filesLets talk about how to use files

Your program starts in main, computes, Your program starts in main, computes, then maybe prints out something before then maybe prints out something before closing upclosing up

Would be great if can save results Would be great if can save results somewheresomewhere Hey lets use files Hey lets use files


File manipulationsFile manipulations

Working with filesWorking with files

Reading filesReading files

Writing filesWriting files


Please notePlease note

One of the great things about file One of the great things about file manipulation on java is that it is the manipulation on java is that it is the same on same on WindowsWindows LinuxLinux MacMac

If done rightIf done right


FileFile

Basic object is called FileBasic object is called File

File data = new File(“test.txt”);File data = new File(“test.txt”);

It will look in the same directory the java It will look in the same directory the java file is sitting in for the test filefile is sitting in for the test file

Calling: data.getAbsolutePath()Calling: data.getAbsolutePath() Will print out the local version of the full path Will print out the local version of the full path

to the fileto the file


Directories Directories

If your File object is a directoryIf your File object is a directory The list method returns an array of The list method returns an array of

String file names, String file names, listFiles returns an array of File listFiles returns an array of File

objectsobjects


limitationslimitations

The File object has a limited number The File object has a limited number of useful methodsof useful methods

None which can actually write None which can actually write something to itsomething to it

Need to use higher level class to Need to use higher level class to work with file contentswork with file contents


Dealing with textDealing with text

When dealing with text output/input When dealing with text output/input can usecan use

PrintWriter to write to a filePrintWriter to write to a file


codecode

PrintWriter pw = new PrintWriter(new PrintWriter pw = new PrintWriter(new FileWriter(new File("Test.txt")));FileWriter(new File("Test.txt")));

What is FileWriter ?What is FileWriter ?

Lets pull up the APILets pull up the API


Helper class to help make sure things Helper class to help make sure things are written efficientlyare written efficiently

Don’t forget to close the file handle Don’t forget to close the file handle when donewhen done

And flush if using a buffered handleAnd flush if using a buffered handle


Ok lets write some codeOk lets write some code

Main programMain program

Will write a 3 line poem (yes you need to Will write a 3 line poem (yes you need to write one now) to a test.txt filewrite one now) to a test.txt file

Notice how your have to add try catch to Notice how your have to add try catch to handle certain declared exceptions ??handle certain declared exceptions ??


Run codeRun code

Confirm that the file has been Confirm that the file has been createdcreated

Now write another class to read the Now write another class to read the filefile


How would you adopt the reader to How would you adopt the reader to find something in the file ??find something in the file ??


For each line readFor each line read

Look for somethingLook for something

See String API for helper methodsSee String API for helper methods

Now write the code Now write the code


Next upNext up

InterfacesInterfaces InheritanceInheritance Abstract ClassesAbstract Classes PolymorphismPolymorphism GenericsGenerics


Two dimensionsTwo dimensions

You can also initialize the inner array as a You can also initialize the inner array as a separate call.separate call.

Doesn’t have to be congruous memory Doesn’t have to be congruous memory locationslocations

int [][]example = new int[5][];int [][]example = new int[5][];

for (int i=0;i<5;i++){for (int i=0;i<5;i++){

example[i] = new int[i+1];example[i] = new int[i+1];

}}


InterfaceInterface

An interface is a special class that An interface is a special class that defines the behavior of other classesdefines the behavior of other classes

Example Example How many mp3 players are on the How many mp3 players are on the

market ?market ?


Mp3 playersMp3 players

No matter what type of mp3 player you No matter what type of mp3 player you buy you expect certain behaviorbuy you expect certain behavior

PlayPlay Forward(next song)Forward(next song) Rewind(last song)Rewind(last song) RandomRandom

Think of your ownThink of your own


If I want to program a bunch of mp3 If I want to program a bunch of mp3 players and want to force all of them players and want to force all of them to have some minimum behavior I to have some minimum behavior I would encode that as an interfacewould encode that as an interface

Here is an example:Here is an example:


codecode

public interface mp3player {public interface mp3player {

public boolean play();public boolean play();

public boolean rewind();public boolean rewind();

public boolean forward();public boolean forward();

public int getSongCount();public int getSongCount();

public boolean deleteAll();public boolean deleteAll();

}}


analysisanalysis

Basically am defining ideasBasically am defining ideas

Would add comments to each what Would add comments to each what they are supposed to be doing they are supposed to be doing (expected behavior(expected behavior

Then any class which wants to be Then any class which wants to be nice, would agree to behave this waynice, would agree to behave this way


Code: IpodMP3Code: IpodMP3

Say we want to create a really cool Say we want to create a really cool mapple ipod playermapple ipod player

Want to stick to the mp3 behaviorWant to stick to the mp3 behaviorpublic class Ipodmp3 implements mp3player public class Ipodmp3 implements mp3player { ..{ ..

This means that we need to define This means that we need to define those methods for this specific classthose methods for this specific class


Note Note

Can implement as many interfaces as you likeCan implement as many interfaces as you like Will notice them in the api when you look at Will notice them in the api when you look at

the standard librariesthe standard libraries Compiler will check and complain if you don’t Compiler will check and complain if you don’t

implement all the methods you are promising implement all the methods you are promising in the interface you implimentin the interface you impliment

Nothing actually checks that you are doing the Nothing actually checks that you are doing the correct thing….that is up to the programmercorrect thing….that is up to the programmer


GASP!GASP!

Question: so what does : Question: so what does : Ipodmp3 player1 = new Ipodmp3 ();Ipodmp3 player1 = new Ipodmp3 ();player1.play()player1.play()actually do ??actually do ??

Answer: Maybe erase your hard Answer: Maybe erase your hard drive…look at the source code drive…look at the source code


IteratorsIterators

Many of the classes in Java represent Many of the classes in Java represent a collection of itemsa collection of items

Some have orderSome have order Some don’t have orderSome don’t have order

All the students in one roomAll the students in one room Alphabetical listAlphabetical list Bag of names (raffle)Bag of names (raffle)


Two typesTwo types

Here is a general Iterator ideaHere is a general Iterator idea

Get the iterator object from the classGet the iterator object from the class

Can ask the iterator object if it has any Can ask the iterator object if it has any more stuff more stuff

Get the next thingGet the next thing


Inheritance Inheritance

You have a really useful classYou have a really useful class Want to specialize it in more than one Want to specialize it in more than one

wayway

Can either copy paste a bunch of time Can either copy paste a bunch of time and tweak each copyand tweak each copy

Problem if we find a bug, will need to Problem if we find a bug, will need to run to all copies and fix everythingrun to all copies and fix everything


Easier way:Easier way:

Look at all the classes that are related, Look at all the classes that are related, what ideas do they all sharewhat ideas do they all share

Example: what is common between all Example: what is common between all kinds of carskinds of cars

Make that idea the base class, and each Make that idea the base class, and each specialization a sub classspecialization a sub class

Known as inheritance!Known as inheritance!


Inheritance Inheritance

Use the ‘extends’ keywordUse the ‘extends’ keyword Allows you to reuse objectsAllows you to reuse objects

Some issues:Some issues: When do you extend?When do you extend? When do you implement an interface?When do you implement an interface?


ExampleExample

Geneal idea of an AnimalGeneal idea of an Animal Can code it as class AnimalCan code it as class Animal Then have specific codeThen have specific code

class Horse extends Animalclass Horse extends Animal class Whale extends Animalclass Whale extends Animal

What ever methods are the same in both What ever methods are the same in both would be coded in the Animal class, would be coded in the Animal class, specific methods (numberLegs() would be specific methods (numberLegs() would be defined in the specific subclass)defined in the specific subclass)


Super constructorsSuper constructors

When refering to parent class (Animal)When refering to parent class (Animal) Use super keyword in subclass constructor:Use super keyword in subclass constructor: public Horse(String aName)public Horse(String aName) {{ super(aName); // calls superclass constructorsuper(aName); // calls superclass constructor //rest of your stuff here//rest of your stuff here }} Call to super must be first statement in subclass Call to super must be first statement in subclass

constructorconstructor If subclass constructor doesn't call super, If subclass constructor doesn't call super,

superclass must have constructor without superclass must have constructor without parametersparameters


Polymorphism Polymorphism

This is just fancy word that tells you java This is just fancy word that tells you java will figure out the following code:will figure out the following code:

Animal A = new Horse(“tom”);Animal A = new Horse(“tom”);

So although A is really a horse, it can be So although A is really a horse, it can be refered to by parent handle.refered to by parent handle.

This would be illigal:This would be illigal: Horse A = new Whale();Horse A = new Whale(); Why ?Why ?


NextNext

Imagine you have a class which has variable Imagine you have a class which has variable members of a specific typemembers of a specific type

Example:Example:

Have a list of numbers, say a list of zip codes Have a list of numbers, say a list of zip codes which you have sent packages in the last X which you have sent packages in the last X monthsmonths

What if you want to change zip codes to Strings What if you want to change zip codes to Strings because you are now sending packages to because you are now sending packages to canadacanada


2 solutions2 solutions

Copy paste code and replace all ints Copy paste code and replace all ints with Stringswith Strings

Debug like crazyDebug like crazy

…….or use Generics.or use Generics


Basic ideaBasic idea

Tell java you are dealing with some Tell java you are dealing with some type without know what it istype without know what it is

Can set some rules on itCan set some rules on it

When you create an instance of the When you create an instance of the object you will tell java what you wantobject you will tell java what you want


CodeCode

public class shoppingList<T> {public class shoppingList<T> {

private ArrayList<T> theList;private ArrayList<T> theList;

shoppingList(){shoppingList(){theList = new ArrayList<T>();theList = new ArrayList<T>();

}}

public void addItem(T item){public void addItem(T item){theList.add(item);theList.add(item);

}}

public int getNumberOnList(){public int getNumberOnList(){return theList.size();return theList.size();

}}

public T getItemAt(int location){public T getItemAt(int location){return theList.get(location);return theList.get(location);

}}}}


Code 1Code 1

//once you get previous screen running at the following //once you get previous screen running at the following methodmethod

public void showType() { public void showType() { System.out.println("Type of T is " + System.out.println("Type of T is " + ob.getClass().getName()); ob.getClass().getName()); } }


Usage Usage

shoppingList<Integer> e1; shoppingList<Integer> e1;

e1 = new shoppingList<Integer>; e1 = new shoppingList<Integer>; e1.add(15); e1.add(15);

int v = e1.getItemAt(0); int v = e1.getItemAt(0);

Write a main to test the idea of genericsWrite a main to test the idea of generics


Example2Example2

class Example2<T, V> { class Example2<T, V> { T ob1; T ob1; V ob2; V ob2;

Example2(T o1, V o2) { Example2(T o1, V o2) { ob1 = o1; ob1 = o1; ob2 = o2; ob2 = o2; } }

T getob1() { T getob1() { return ob1; return ob1; } }

V getob2() { V getob2() { return ob2; return ob2; } } }}


Example 3Example 3

class Example3<Q extends Number> { class Example3<Q extends Number> {

Q[] nums; // array of Number or subclass Q[] nums; // array of Number or subclass

Stats(Q[] o) { Stats(Q[] o) { nums = o; nums = o; } }

double sum() { double sum() { double sum = 0.0; double sum = 0.0; for(int i=0; i < nums.length; i++) for(int i=0; i < nums.length; i++) sum += nums[i].doubleValue(); sum += nums[i].doubleValue(); return sum; return sum; } } } }


Usage Usage

Double dnums[] ={ 1.1, 2.2, 3.3, 4.4, 5.5 }; Double dnums[] ={ 1.1, 2.2, 3.3, 4.4, 5.5 };

Example3<Double> dob = new Example3<Double> dob = new Example3<Double>(dnums); Example3<Double>(dnums);

double w = dob.sum(); double w = dob.sum();

System.out.println("dob sum is " + w); System.out.println("dob sum is " + w);


Example4Example4class TwoD { class TwoD { int x, y; int x, y; TwoD(int a, int b) { TwoD(int a, int b) { x = a; x = a; y = b; y = b; } } } }

class ThreeD extends TwoD { class ThreeD extends TwoD { int z; int z; ThreeD(int a, int b, int c) { ThreeD(int a, int b, int c) { super(a, b); super(a, b); z = c; z = c; } } } }

class FourD extends ThreeD { class FourD extends ThreeD { int t; int t; FourD(int a, int b, int c, int d) { FourD(int a, int b, int c, int d) { super(a, b, c); super(a, b, c); t = d; t = d; } } } }


class Coords<T extends TwoD> { class Coords<T extends TwoD> {

T[] coords; T[] coords;

Coords(T[] o) { coords = o; } Coords(T[] o) { coords = o; }

} }


static void showXY(Coords<?> c) { static void showXY(Coords<?> c) { System.out.println("X Y Coordinates:"); System.out.println("X Y Coordinates:"); for(int i=0; i < c.coords.length; i++) for(int i=0; i < c.coords.length; i++) System.out.println(c.coords[i].x + " " System.out.println(c.coords[i].x + " " + +

c.coords[i].y); c.coords[i].y); System.out.println(); System.out.println(); } }


static void showXYZ(Coords<? extends ThreeD> c) { static void showXYZ(Coords<? extends ThreeD> c) { System.out.println("X Y Z Coordinates:"); System.out.println("X Y Z Coordinates:"); for(int i=0; i < c.coords.length; i++) for(int i=0; i < c.coords.length; i++) System.out.println(c.coords[i].x + " " + System.out.println(c.coords[i].x + " " + c.coords[i].y + " " + c.coords[i].y + " " + c.coords[i].z); c.coords[i].z); System.out.println(); System.out.println(); } }


static void showAll(Coords<? extends FourD> c) { static void showAll(Coords<? extends FourD> c) { System.out.println("X Y Z T Coordinates:"); System.out.println("X Y Z T Coordinates:"); for(int i=0; i < c.coords.length; i++) for(int i=0; i < c.coords.length; i++) System.out.println(c.coords[i].x + " " + System.out.println(c.coords[i].x + " " + c.coords[i].y + " " + c.coords[i].y + " " + c.coords[i].z + " " + c.coords[i].z + " " + c.coords[i].t); c.coords[i].t); System.out.println(); System.out.println(); } }


Using in methodsUsing in methods

Just learn how to read the following:Just learn how to read the following:

static <T, V extends T> boolean isIn(T x, V[] y) { static <T, V extends T> boolean isIn(T x, V[] y) {

for(int i=0; i < y.length; i++) for(int i=0; i < y.length; i++) {{

if(x.equals(y[i])) return true; if(x.equals(y[i])) return true; }}

return false; return false;

} }


Hope you had fun learning this!Hope you had fun learning this!

Documents

Shlomo Hershkop 2007 1 Advanced Review. Shlomo Hershkop 20072 Advanced Review Time classes Time classes Date Classes Date Classes File input/output File