11.24观察者模式

package tutor21;

import java.util.ArrayList;

public class Client {

    public static void main(String args[]) {

        MySubject subject = new Stock();
        MyObserver obs1;
        obs1=new Holders();
        subject.attach(obs1);

        System.out.println("股票上涨");
        subject.change(5);

        System.out.println("股票下跌");
        subject.change(-5);
    }

}
 class Holders implements MyObserver {

    public void response(int rate) {

        if(rate>=5) {

            System.out.println("股票上涨，买股票");

        }else if(rate<=-5){

            System.out.println("股票下跌，大哭一场");

        }

    }

}
interface MyObserver {

    void response(int rate);

}
abstract class MySubject {

    protected ArrayList<MyObserver> observers = new ArrayList<MyObserver>();

//注册方法

    public void attach(MyObserver observer) {

        observers.add(observer);

    }

//注销方法

    public void detach(MyObserver observer) {

        observers.remove(observer);

    }

//抽象通知方法

    public abstract void change(int rate);

}
class Stock extends MySubject {

    public void change(int rate) {

        for(Object obs : observers) {

            ((MyObserver)obs).response(rate);

        }

    }

}