How to replace a substring inside a string by another one ?

This example describes how replace method of java String class can be used to replace character or substring by new one.

public class StringReplaceEmp{
   public static void main(String args[]){
      String str = "Hello World";
      System.out.println( str.replace( 'H','W' ) );
      System.out.println( str.replaceFirst("He", "Wa") );
      System.out.println( str.replaceAll("He", "Ha") );
   }
}


Result
The above code sample will produce the following result.

Wello World
Wallo World
Hallo World