import java.util.ArrayList;

import java.util.Iterator;

/* 抽象观察者类 */

abstract class Observer {

    public abstract void update();

}

/* 抽象被观察主题类 */

abstract class Subject{

    private ArrayList obs_list = new ArrayList();

    public void attach(Observer obs) {

        obs_list.add(obs);

    }

    public void Detach(Observer obs) {

        obs_list.remove(obs);

    }

    public void notifyObs() {

        for (Iterator iter = obs_list.iterator(); iter.hasNext();) {

            Observer obs = (Observer) iter.next();

            obs.update();

        }

    }

}

/* 具体观察者类 */

class ConcreteObserver extends Observer {

    private String obs_name;

    private ConcreteSubject cc_subj;

    public ConcreteObserver(String obs_name, ConcreteSubject cc_subj) {

        this.obs_name = obs_name;

        this.cc_subj = cc_subj;

    }

    public void update() {

        if (cc_subj.getStatus() == 1) {

            System.out.println("Boss come back, " + obs_name + " turn off screen!");

        } else {

            System.out.println("Boss go out, " + obs_name + " turn on screen!");

        }

    }

}

/* 具体观察主题类 */

class ConcreteSubject extends Subject {

    private int status;

    public ConcreteSubject(int status) {

        this.status = status;

    }

    public int getStatus() {

        return status;

    }

    public void setStatus(int status) {

        if (status != this.status) {

            this.status = status;

            super.notifyObs();

        }

    }

}

public class Observer_Test{

    public static void main(String[] args) {

        ConcreteSubject cc_sub = new ConcreteSubject(0);

        ConcreteObserver cc_obs1 = new ConcreteObserver("E1", cc_sub);

        ConcreteObserver cc_obs2 = new ConcreteObserver("E2", cc_sub);

        ConcreteObserver cc_obs3 = new ConcreteObserver("E3", cc_sub);

        cc_sub.attach(cc_obs1);

        cc_sub.attach(cc_obs2);

        cc_sub.attach(cc_obs3);

        cc_sub.setStatus(1); //status changed to 1

        System.out.println("---------------------------------------");

        cc_sub.setStatus(0); //status changed to 0

    }

}