String Objects are Immutable

String objects are immutable which means that once a String has been constructed, it never can be changed. This has many advantages in making programs understandable and reliable. For example, if a method has a reference to a String, that String will always contain the same characters, no matter what other methods are called and what they do. For this reason, a program that does only a moderate amount of character manipulation should do it all using class String.

Examine the following program:

public class Immutable
{

  public static void mysteryMethod( String data )
  {
    . . . .
  }

  public static void main ( String[] args )
  {
    String str = "An Immutable String" ;
    mysteryMethod( str );
    System.out.println( str );
  }
}