观察者模式(bilibili)

package it.heima.netty.observer;

public interface Subject {

    /** 注册观察者 */
    void registryObserver(Observer observer);

    /** 移除观察者 */
    void removeObserver(Observer observer);

    /** 通知观察者 */
    void notifyObservers();
}

package it.heima.netty.observer;

public interface Observer {

    /**
     * 观察者获得主题消息
     * @param msg
     */
    void update(String msg);
}

package it.heima.netty.observer;

import java.util.ArrayList;
import java.util.List;

/**
 * 福利彩票
 */
public class WelfareLottery implements Subject {

    /** 主题存储观察者集合 */
    private List<Observer> observerList;

    /** 主题消息 */
    private String msg;

    public WelfareLottery(String msg){
        this.observerList = new ArrayList<Observer>();
        this.msg = msg;
    }

    /**
     * 存放观察者
     * @param observer
     */
    public void registryObserver(Observer observer) {
        this.observerList.add(observer);
    }

    /**
     * 删除观察者
     * @param observer
     */
    public void removeObserver(Observer observer) {
        int index = this.observerList.indexOf(observer);
        if(-1 != index){
            this.observerList.remove(index);
        }
    }

    /**
     * 通知观察者们
     */
    public void notifyObservers() {
        for (Observer observer : observerList) {
            observer.update(msg);
        }
    }
}

package it.heima.netty.observer;

public class WelfareLotteryBuyer implements Observer {

    /** 观察者姓名*/
    private String name;

    /** 主题 */
    private Subject subject;

    public WelfareLotteryBuyer(String name, Subject subject) {
        this.name = name;
        this.subject = subject;
        this.subject.registryObserver(this);
    }

    public void update(String msg) {
        System.out.println("观察者" + name + "订阅消息:" + msg);

    }
}

package it.heima.netty.observer;

public class Main {

    public static void main(String[] args) {
        Subject subject = new WelfareLottery("中奖号码: 12323");

        Observer observer1 = new WelfareLotteryBuyer("张明", subject);
        Observer observer2 = new WelfareLotteryBuyer("张飞", subject);
        Observer observer3 = new WelfareLotteryBuyer("张涛", subject);

        subject.removeObserver(observer1);
        subject.notifyObservers();

    }
}