设计模式---观察者模式

观察者模式:

                   定义了一种一对多的依赖关系，让多个观察者对象同时监听某一个主题对象。

                    这个主题对象在状态上发生变化时，会通知所有观察者对象，让它们能够自动更新自己。

//抽象观察者角色

public interface Watcher

{

    public void update(String str);

 

}

 

//抽象主题角色，watched：被观察

public interface Watched

{

    public void addWatcher(Watcher watcher);

 

    public void removeWatcher(Watcher watcher);

 

    public void notifyWatchers(String str);

 

}

 

public class ConcreteWatcherimplements Watcher

{

    @Override

    public void update(String str)

    {

        System.out.println(str);

    }

}

import java.util.ArrayList;

import java.util.List;

public class ConcreteWatchedimplements Watched

{

    // 存放观察者

    private List<Watcher> list = new ArrayList<Watcher>();

 

    @Override

    public void addWatcher(Watcher watcher)

    {

        list.add(watcher);

    }

 

    @Override

    public void removeWatcher(Watcher watcher)

    {

        list.remove(watcher);

    }

 

    @Override

    public void notifyWatchers(String str)

    {

        // 自动调用实际上是主题进行调用的

        for (Watcher watcher : list)

        {

            watcher.update(str);

        }

    }

 

}

public class Test

{

    public static void main(String[] args)

    {

        Watched girl = new ConcreteWatched();

        

        Watcher watcher1 = new ConcreteWatcher();

        Watcher watcher2 = new ConcreteWatcher();

        Watcher watcher3 = new ConcreteWatcher();

        

        girl.addWatcher(watcher1);

        girl.addWatcher(watcher2);

        girl.addWatcher(watcher3);

        

        girl.notifyWatchers("开心");

    }

 

}