String, StringBuilder and StringBuffer-An Introduction

               A Collection of characters forms a String. The characters may be alphabets, special characters or numbers too.

Some of the built-in classes are

• ·       String
• ·       StringBuilder
• ·       StringBuffer

Common methods for each class are given below.

String:

              String is a sequence of characters which are immutable. To create an object using String literally, use the below code.

String a =” Welcome”;

If you want to create a string object using “new” keyword, just follow the code given as follows.

String a = new String (“Welcome”);

If you are using character array, this code helps you.

char[] cA = { 'W', 'e', 'l', 'c', 'o',’m’,’e’ };

String a = new String(cA);

Let us code an example for Byte Array.

Byte[] bA = {87,101,108,99,111,109,101}; //ASCII value for welcome

String b = new String (bA);

Common methods for String:

import java.lang.String.*;

class StringEg

{

 public static void main(String args[])

 {

  String a = new String ("Welcome to the world of Java");

  System.out.println("The String is:"+a);

  System.out.println("The length of the String is:"+a.length());

  System.out.println("The 3rd position character in the String is:"+a.charAt(3));

 

  System.out.println("The substring index is:"+a.indexOf("world"));

  System.out.println("The String in lowercase is:"+a.toLowerCase());

  System.out.println("The String in Uppercase is:"+a.toUpperCase());

  System.out.println("The concatenated string is:"+a.concat("Programming "));

  }

}

Output:

C:\raji\blog>javac StringEg.java

C:\raji\blog>java StringEg

The String is:Welcome to the world of Java

The length of the String is:28

The 3rd position character in the String is:c

The substring index is:15

The String in lowercase is:welcome to the world of java

The String in Uppercase is:WELCOME TO THE WORLD OF JAVA

The concatenated string is:Welcome to the world of JavaProgramming

Note: String is thread safe.

StringBuilder:

              This string content can be modified. It has mutable sequence of characters. The methods in this ‘StringBuilder’ is given below.

Methods:

Insert(): it inserts the given string into the specified postion.

Delete(): it removes a specified sub string.

Append(): This function appends the given string into the string.

Reverse():This reverses the entire string.

toString(): It converts the StringBuilder into String.

Note: It is mutable but not thread safe. Suitable for single thread operations.

StringBuffer:

              It handles multi thread in safe manner. The common methods are listed below.

Methods:

toString(): This function converts the StringBuffer into String.

Append():It adds the given string into StringBuffer.

Reverse():The entire String is reversed.

Insert(): It adds the string into specific position.

Delete():It removes the set of characters.

Replace(): It replaces the set of characters.

It is useful for multi-threaded environments.