To Replace a Substring inside a String by Another One

Here is a Java Program to replace a substring inside a string by another 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") );
   }
}

Output of Above Java Program
Wello World
Wallo World
Hallo World