// 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
*/