设计模式- 观察者模式

定义对象间的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发生改变时，会通知所有观察者对象，使它们能够自动更新自己。

例子：
定义观察者与被观察者

public interface Watcher{    public void update();}

public class Mother implements Watcher{    @Override    public void update()    {        System.out.println("妈妈在看着");    }}

public class Father implements Watcher{    @Override    public void update()    {        System.out.println("爸爸在看着");    }}

public interface Watched{  public void addWatcher(Watcher watcher);  public void removeWatcher(Watcher watcher);  public void notifyWatcher();}

public class Baby implements Watched{    List<Watcher> watcherList = new ArrayList<>();    @Override    public void addWatcher(Watcher watcher)    {        watcherList.add(watcher);    }    @Override    public void removeWatcher(Watcher watcher)    {        if (watcherList.contains(watcher))        {            watcherList.remove(watcher);        }    }    @Override    public void notifyWatcher()    {        for (Watcher watcher : watcherList)        {            watcher.update();        }    }}

测试类

    public static void main(String[] args)    {        Father father;        Baby baby = new Baby();        father = new Father();        baby.addWatcher(father);        baby.addWatcher(new Mother());        baby.notifyWatcher();        System.out.println();        baby.removeWatcher(father);        baby.notifyWatcher();    }

结果
爸爸在看着
妈妈在看着

妈妈在看着

我的理解就是，定义观察者，确定在一定情况下，要做什么
然后呢，定义被观察者，它可以增加删除它的观察者，并可通知观察者何时可以行动

使用RxJava实现
下面的demo ，是先生成被观察者，负责通知观察者变化。观察者做一些反馈

public class BabyObservable extends Observable{    public void cry()    {        System.out.println("宝宝哭了");        setChanged();        notifyObservers();    }}

public class FatherObserver implements Observer{    FatherObserver (BabyObservable babyObservable){        babyObservable.addObserver(this);    }    @Override    public void update(Observable observable, Object data)    {        System.out.println("爸爸过了照顾了");    }}

public class MotherObserver implements Observer{    MotherObserver (BabyObservable babyObservable)    {        babyObservable.addObserver(this);    }    @Override    public void update(Observable observable, Object data)    {        System.out.println("妈妈过了照顾了");    }}

public class BabyTest{    public static void main(String[] args) throws Exception    {        BabyObservable mBabyObservable = new BabyObservable();        FatherObserver fatherObserver = new FatherObserver(mBabyObservable);        MotherObserver motherObservaer = new MotherObserver(mBabyObservable);        mBabyObservable.cry();    }}

结果：
宝宝哭了
妈妈过了照顾了
爸爸过了照顾了