观察者模式

当股票的价格上涨或下降5%时，会通知持有该股票的股民，当股民听到价格上涨的消息时会买股票，当价格下降时会大哭一场。

 

抽象目标类：

package com;

public class ConcreteSubject extends Subject{
    @Override
    public void attach(Observer observer) {
        observers.add(observer);
    }

    @Override
    public void detach(Observer observer) {
        observers.remove(observer);
    }

    @Override
    public void down() {
        for (Object obs:observers){
            ((Observer)obs).cry();
        }
    }

    @Override
    public void up() {
        for (Object obj:observers){
            ((Observer)obj).buy();
        }
    }

}

　　具体目标类

package com;

import java.util.ArrayList;

public abstract class Subject {
    protected ArrayList observers= new ArrayList();
    public abstract void attach(Observer observer);
    public abstract void detach(Observer observer);
    public abstract void down();
    public abstract void up();
}

 

　抽象观察者类：

package com;

public interface Observer {
    void buy();
            void cry();
}

　　

具体观察这类：　

 

package com;

public class humin implements Observer{

    @Override
    public void buy() {
        System.out.println("股票上涨，购入");
    }

    @Override
    public void cry() {
        System.out.println("股票下跌，哭");
    }
}

　　客户端

package com;

public class Client {
    public static void main(String[] args) {
        Observer gumin1,gumin2,gumin3;
        gumin1=new humin();
        gumin2=new humin();
        gumin3=new humin();

        Subject gupiao =new ConcreteSubject();
        gupiao.attach(gumin1);
        gupiao.attach(gumin2);
        gupiao.attach(gumin3);
        gupiao.up();
        gupiao.down();
    }
}