行为型模式（三）：Observer ( 观察者模式 )

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

//被观察者接口
interface Watched{
    public void addWatcher(Watcher watcher);
    public void removeWatcher(Watcher watcher);
    public void notifyAllWatchers(String str);
}
//被观察者实现类
class ConcreteWatched implements Watched{
    List<Watcher> watchers=new ArrayList<Watcher>();
    @Override//添加观察者
    public void addWatcher(Watcher watcher) {
        watchers.add(watcher);
    }
    @Override//通知观察者
    public void notifyAllWatchers(String str) {
        for(Watcher watcher:watchers){
            watcher.update(str);
        }
    }
    @Override//删除观察者
    public void removeWatcher(Watcher watcher) {
        watchers.remove(watcher);
    }
}
//观察者接口
interface Watcher{
    public void update(String str);
}
//观察者实现类
class ConcreteWatcher implements Watcher{
    @Override//观察者动作
    public void update(String str) {
        System.out.println(str);
    }
}


public class Test {
    public static void main(String[] args) {
        Watched girl=new ConcreteWatched();
        Watcher boy1=new ConcreteWatcher();
        Watcher boy2=new ConcreteWatcher();
        Watcher boy3=new ConcreteWatcher();
        girl.addWatcher(boy1);
        girl.addWatcher(boy2);
        girl.addWatcher(boy3);
        girl.notifyAllWatchers("很开心~~~");
        girl.removeWatcher(boy2);
        girl.notifyAllWatchers("不开心~~~~");
    }
}