实际订阅者 肯定是在数据库里面的    根据订阅者订阅的天气分类等 查出  订阅者进行发布

定义三个observer列表~

其实就下雨下雪晴天等等这些信息，是来源于数据，即来自己被观察者的依赖。通常是交给第三方类处理。

设计一种数据结构，方便用户订阅和系统反馈

public class WheatherSubject {

    private List<WheatherObserver> mObservers = new ArrayList<>();
    private String wheather;

    public final static String SNOW = "下雪";
    public final static String RAIN = "下雨";
    public final static String SUNNY = "晴";

    public String getWheather() {
        return wheather;
    }

    public void setWheather(String wheather) {
        this.wheather = wheather;
        notifyObservers(wheather);
    }

    public void attach(WheatherObserver observer) {
        mObservers.add(observer);
    }

    public void detach(WheatherObserver observer) {
        mObservers.remove(observer);
    }

    public void notifyObservers(String wheather) {
        for (WheatherObserver observer : mObservers) {
            if (observer.getWheathers().size() < 1 || observer.getWheathers().contains(wheather)) {
                observer.update(wheather);
            }
        }
    }
}

public class WheatherObserver {

    private ArrayList<String> mWheathers;

    public WheatherObserver(String... wheathers) {
        mWheathers = new ArrayList<>();
        mWheathers.addAll(Arrays.asList(wheathers));
    }

    public ArrayList<String> getWheathers() {
        return mWheathers;
    }

    public void setWheathers(ArrayList<String> wheathers) {
        if (mWheathers != null) {
            mWheathers.clear();
            mWheathers.addAll(wheathers);
        }
    }

    public void update(String wheather){
        System.out.print(wheather);
        Log.i("fy",wheather);
    }
}

public class WheaterClint {

    public static void main(String[] args){

        WheatherSubject subject = new WheatherSubject();
        WheatherObserver observerAll = new WheatherObserver();
        WheatherObserver observerSnow = new WheatherObserver(WheatherSubject.SNOW);
        WheatherObserver observerSnowAndRain = new WheatherObserver(WheatherSubject.SNOW,WheatherSubject.RAIN);

        subject.attach(observerAll);
        subject.attach(observerSnow);
        subject.attach(observerSnowAndRain);

        subject.setWheather(WheatherSubject.RAIN);
    }
}