package polimorphism;

class Actor {
  public void act() {}
}

class HappyActor extends Actor {
  public void act() { System.out.println("HappyActor"); }
}

class SadActor extends Actor {
  public void act() {  System.out.println("SadActor"); }
}

class Stage {
  private Actor actor = new HappyActor();
  public void changeRole() { actor = new SadActor(); }
  public void performPlay() { actor.act(); }
}

public class Transformation {
  public static void main(String[] args) {
    Stage stage = new Stage();
    stage.performPlay();
    stage.changeRole();
    stage.performPlay();
  }
}