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") );
    	}
    }