状态模式

State.java

import static com.mceiba.util.Print.*;

class Actor{
	public void act() {}
}
class HappyActor extends Actor{
	public void act() { println("HappyActor"); }
}
class SadActor extends Actor{
	public void act() { println("SadActor"); }
}
class Stage{
	private Actor actor = new HappyActor();
	public void change() { actor = new SadActor(); }
	public void performPlay() { actor.act(); }
}
public class State{
	public static void main(String[] args){
		Stage stage = new Stage();
		stage.performPlay();
		stage.change();
		stage.performPlay(); 
	}
}