mutable string
 Source Code
// Contributed by - Anuj Das ( GC College, Silchar - @ Department of Computer Science )

class StringBufferMethods {
  public static void main(String[ ] args) {
    StringBuffer str = new StringBuffer("Human");
        System.out.println(str);

/*------------------------------------------------------------------------------------------------------------------------
  public synchronized StringBuffer append(String s)  --> Add specified string at the end of the existing string.
  And it modifies the existing string as StringBuffer creates mutable strings.
-------------------------------------------------------------------------------------------------------------------------*/
    str.append("Being");
    System.out.println(str);



/*	public synchronized StringBuffer insert(int offset, String s)  --> Inserts at specified string at specified index.	 */
    str.insert(0,"Hello");
    System.out.println(str);



/*------------------------------------------------------------------------------------------------------------------------
  public synchronized StringBuffer replace(int startIndex, int endIndex, String str)
  It is used to replace the string from specified startIndex and endIndex.
  1. Here, from index 1 to 15 the substring is "HumanBeing" which is replaced with "World"
-------------------------------------------------------------------------------------------------------------------------*/
    str.replace(5,15,"World");
    System.out.println(str);



/*------------------------------------------------------------------------------------------------------------------------
  public synchronized StringBuffer delete(int startIndex, int endIndex)
  It is used to delete the string from specified startIndex and endIndex-1.
-------------------------------------------------------------------------------------------------------------------------*/
    str.delete(5,9);
    System.out.println(str);



/*	public synchronized StringBuffer reverse() --> It is used to reverse the string.	*/
    str.reverse();
    System.out.println(str);



/*	public int capacity() -->  It is used to return the current capacity.	*/
    System.out.println("Capacity:  " + str.capacity());



/*--------------------------------------------------------------------------------------------------------------
  *NOTE:  Some Methods of String class can also be used:
  1. charAt()
  2. length()
  3. substring()
  4. indexOf()
----------------------------------------------------------------------------------------------------------------*/

  }
}