Strings, I/O, Formatting, and Parsing. String, StringBuilder, and StringBuffer

Strings, I/O,Formatting,and Parsing

String, StringBuilder, and StringBuffer

The String Class

• String are immutable objects• Create an instance of String with

the keyword "new“• Example:

– String s = new String();– String s = new String("abcdef");– String s = "abcdef";

The String Class

The String Class

The String Class

The String Class

• Another example:

The String Class

• Output:

The String Class

• And now?

The String Class

• Example:

The String Class

• Que imprime?:

The String Class

• Imprime "spring winter spring summer".

Important facts about String and memory

• JVM reserve a special area called "Sreing constant pool”

• When the compiler encounters a string literal, it checks the pool to see if it exists. If found, the literal reference to the new addresses the existing chain (the existing chain has an additional reference.) [Immutable]

new String

String Class Methods

String Methods

• public char charAt(int index)

String x = "airplane";System.out.println( x.charAt(2) );

// output ‘r’

String Methods

• public String concat(String s)

String x = "taxi";System.out.println( x.concat("

cab") );

// output is "taxi cab"

String Methods

• public boolean equalsIgnoreCase(String s)

String x = "Exit";System.out.println(x.equalsIgnoreCase("EXIT");

// is "true“

System.out.println(x.equalsIgnoreCase("tixe")); // is "false"

String Methods

• public int length()

String x = "01234567";System.out.println( x.length() ); // returns "8"

String Methods

• public String replace(char old, char new)

String x = "oxoxoxox";System.out.println( x.replace('x', 'X') ); // output is "oXoXoXoX"

String Methods

• public String substring(int begin)• public String substring(int begin, int

end)

String x = "0123456789"; System.out.println( x.substring(5) ); // output is "56789"System.out.println( x.substring(5, 8)); // output is "567"

String Methods

• public String toLowerCase()

String x = "A New Moon";System.out.println( x.toLowerCase()

);

// output is "a new moon"

String Methods

• public String toUpperCase()

String x = "A New Moon";System.out.println( x.

toUpperCase() );

// output is “A NEW MOON"

String Methods

• public String trim()

String x = " hi ";System.out.println( x + "x" ); // result is " hi x"System.out.println( x.trim() + "x"); // result is "hix"

The StringBuffer and StringBuilder Classes

• Java.lang.StringBuilder and java.lang.StringBuffer classes should be used when making several modifications to the strings.

• Unlike String, objects of type StringBuffer and StringBuilder can be modified again and again without leaving behind discarded objects

• A common use of StringBuffer and StringBuilder is on file I / S

StringBuffer vs. StringBuilder

• The StringBuilder class was added in Java 5.

• StringBuilder is Not thread safe. In other words, their methods are not synchronized (Chapter 9)

• Sun recommends that StringBuilder instead of StringBuffer whenever possible because StringBuilder will run faster.

Using StringBuffer and StringBuilder

• StringBuffer

• StringBuilder

Key methods of StringBuffer and

StringBuilder• public synchronized StringBuffer append(String s)

StringBuffer sb = new StringBuffer("set ");sb.append("point");System.out.println(sb); // output is "set point“

StringBuffer sb2 = new StringBuffer("pi = ");sb2.append(3.14159f);System.out.println(sb2); // output is "pi = 3.14159"


StringBuilder• public StringBuilder delete(int

start, int end)

StringBuilder sb = new StringBuilder("0123456789");

System.out.println(sb.delete(4,6)); // output is "01236789"


StringBuilder• public StringBuilder insert(int

offset, String s)

StringBuilder sb = new StringBuilder("01234567");sb.insert(4, "---");System.out.println( sb ); // output is "0123---4567"


StringBuilder• public synchronized StringBuffer

reverse()StringBuffer s = new StringBuffer("A man a plan a canal

Panama");sb.reverse();System.out.println(sb); // output: "amanaP lanac a nalp a nam A"


StringBuilder

• public String toString()

StringBuffer sb = new StringBuffer("test string");System.out.println( sb.toString() ); // output is "test string"

File Navigation and I/O

• File .- The API says that the kind of file is "an abstract representation n of a file and directory path. " The File class is not used for reading or writing data, is used to work at high level, creating new files, search files, delete files, create directories, and working with paths (path).


• FileReader .- This class is used to read character files. The method read() is very low, allowing you to read the entire flow (stream) character. FileReaders often surrounded by objects of more s high level, BufferedReaders, which improves performance and provides the means most convenient to work s with the data.


• BufferedReader.- In comparison with FileReaders n, BufferedReaders read into relatively large data file at a time, and maintains these data in a buffer. When prompted for the next character or line of data is retrieved from memory (minimizes the time) and then perform read operations. In addition s, BufferedReader provides methods more suitable as readLine(), giving the next line of arhiva


• FileWriter.- This class is used for writing character files. His method write() to write character (s) of strings or a file. FileWriter are usually surrounded by writers such as high-level objects or PrintWriters BufferedWriters, which provide better performance and higher, with more method flexible to write the data.


• BufferedWriter.- Compared with FileWriters, writes BufferedWriters relatively large pieces of data from one file at a time, minimizes the number of times of write operations to a file. In addition, the BufferedWriter class provides the method NewLine () that facilitates the creation of line separators automatically.


• PrintWriter.- This class has been improved significantly in Java 5. Because it has new methods and constructors (you can build a PrintWriter from a File or String). New methods like format (), printf () and append () PrintWriter make it very flexible and powerful.

Creating files using the File class

• File type objects are used to represent the current files (but not data files) or directories that exist on a physical computer disk.

Creating files using the File class File

• Solo se a creado el objeto File, no el archivo físico.

Creating files using the File class File

• The above code prints false, true, true• If you run a second time, print: true, false,

true• boolean exists() .- This method returns

true if it finds the specified file.• boolean createNewFile() .- This method

creates a file if it is not exists.• boolean isDirectory() .- This method

returns true if it finds the specified directory

Using FileWriter & FileReader

Using FileWriter & FileReader

• Output:

12 howdyfolks

Writer & Reader Hierarchy

Combining I/O

• Example 1 :

Combining I/O

• Example 2 :

Combining I/O

• Example 3 :

Combining I/O

• Example 4:

Combining I/O

• Example 4:

Combining I/O• Example 5:

Combining I/O• Example 6:

Serialization

• “Save this object and all its instance variables"

Working with ObjectOutputStream &

ObjectInputStream

• ObjectOutputStream.writeObject() • // serialize and write• ObjectInputStream.readObject() • // read and deserialize

Working with ObjectOutputStream &

ObjectInputStream

• Java.io.ObjectOutputStream and java.io.ObjectInputStream classes are high level in the java.io package, and as we learned earlier, that means surrounding the lower classes and java.io.FileInputStream java.io.FileOutputStream

• Example 1:

• Example 2:

Dates, Numbers, and Currency

Working with Dates, Numbers, and

Currencies• java.util.Date The majority of the

method of this kind are obsolete, but can be used as a bridge between the Calendar and DateFormat class. A Date instance can convert the date and time, to milliseconds.

• java.util.Calendar This class provides a variety of methods who help make and manipulate dates and times

Working with Dates, Numbers, and

Currencies• java.text.DateFormat This class

is used to format dates. "01/01/70" -> "January 1 1970”

• java.text.NumberFormat This class is used to format numbers and local currencies (Currencies) for everyone.

The Date Class• Example 1

The Date Class• Example 2

The Calendar Class

The DateFormat Class

The Locale Class

The Locale Class

The Locale Class

The NumberFormat Class

Summary

Parsing, Tokenizing and Formatting

• Simple search:


• Searches using Metacharacters:• source: a12c3e456f• index: 0123456789• pattern: \d

-> regex will tell us that it found digits at positions 1, 2, 4, 6, 7, and 8.

• In case of:• source: “a 1 56 _Z”• index: 0123456789• pattern: \w

-> regex will tell us that it found digits at positions 0, 2, 4, 5, 7, and 8.


• In case of:– source: "cafeBABE"– index: 01234567– pattern: [a-cA-C]

-> returns positions 0, 1, 4, 5, 6.


• Searches using Quantifiers:• + : One or more occurrences• * : Zero or more occurrences• ? : Zero or one occurrences• ^ : For example, with pattern:

“proj1([^,])*” => Give me zero or more characters that aren't a comma


• The Predefined Dot: "any character can serve here."– source: "ac abc a c"– pattern: a.c=> will produce the output

• 3 abc• 7 a c


• Searching Using the Scanner Class:import java.util.*;class ScanIn { public static void main(String[] args) { System.out.print("input: "); System.out.flush(); try { Scanner s = new Scanner(System.in); String token; do { token = s.findInLine(args[0]); System.out.println("found " + token); } while (token != null); } catch (Exception e) { System.out.println("scan exc"); } }}

• The invocation and inputjava ScanIn "\d\d"input: 1b2c335f456

• produce the following:found 33found 45found null


• Tokenizing with String.split()import java.util.*;class SplitTest { public static void main(String[] args) { String[] tokens = args[0].split(args[1]); System.out.println("count " + tokens.length); for(String s : tokens) System.out.println(">" + s + "<"); }}* java SplitTest "ab5 ccc 45 @" "\d"Output: count 4 >ab< > ccc < >< > @<


• Tokenizing with Scanner

FIN

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Strings, I/O, Formatting, and Parsing. String, StringBuilder, and StringBuffer