// polymorphism/Transmogrify.java

// (c)2017 MindView LLC: see Copyright.txt

// We make no guarantees that this code is fit for any purpose.

// Visit http://OnJava8.com for more book information.

// Dynamically changing the behavior of an object

// via composition (the "State" design pattern)

class Actor {

public void act() {}

}

class HappyActor extends Actor {

@Override

public void act() {

System.out.println("HappyActor");

}

}

class SadActor extends Actor {

@Override

public void act() {

System.out.println("SadActor");

}

}

class Stage {

private Actor actor = new HappyActor();

public void change() { actor = new SadActor(); }

public void performPlay() { actor.act(); }

}

public class Transmogrify {

public static void main(String[] args) {

Stage stage = new Stage();

stage.performPlay();

stage.change();

stage.performPlay();

}

}

/* Output:

HappyActor

SadActor

*/