對(duì)象之間是多對(duì)一依賴(lài)的一種設(shè)計(jì)方案，被依賴(lài)的對(duì)象為Subject喉磁，依賴(lài)對(duì)象為Observer，Subject通知Observer變化

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Subject： 負(fù)責(zé)注冊(cè)——通知——撤銷(xiāo)注冊(cè)
Observer:將自己注冊(cè)到被觀(guān)察對(duì)象（Subject）中咖城，被觀(guān)察對(duì)象將觀(guān)察者存放在一個(gè)容器（Container）里十绑。
例子：
設(shè)計(jì)模型：氣象站
特點(diǎn)： 氣象站負(fù)責(zé)溫度，氣壓慧瘤，濕度的收集戴已。等到變化時(shí)通知公告板，廣播公告等锅减。

public interface Subject {
    public void registerObserver(Observer o);
    public void removeObserver(Observer o);
    public void notifyObservers();
}
public interface Observer {
    public void update(float mTemperatrue,float mPressure,float mHumidity);
}
//氣象站
public class WeatherDataSt implements Subject{
    
    private float mTemperatrue;
    private float mPressure;
    private float mHumidity;
    private ArrayList<Observer> mObservers;
    public WeatherDataSt(){
        mObservers=new ArrayList<Observer>();
    }
    public void dataChange(){
        notifyObservers();
    }
    //模擬設(shè)置天氣參數(shù)
    public void setData(float mTemperatrue,float mPressure,float mHumidity){
        this.mTemperatrue=mTemperatrue;
        this.mPressure=mPressure;
        this.mHumidity=mHumidity;
        dataChange();
    }
    @Override
    public void registerObserver(Observer o) {
        // 注冊(cè)
        mObservers.add(o);
    }
    @Override
    public void removeObserver(Observer o) {
        // 撤銷(xiāo)注冊(cè)
        if(mObservers.contains(o))
        {mObservers.remove(o);}
    }
    @Override
    public void notifyObservers() {
              //遍歷所有觀(guān)察者糖儡，通知天氣參數(shù)發(fā)生變化
        for(int i=0,len=mObservers.size();i<len;i++){
            mObservers.get(i).update(mTemperatrue, mPressure, mHumidity);
        }
    }
}

public class CurrentConditions implements Observer {
    private float mTemperatrue;
    private float mPressure;
    private float mHumidity;
    @Override
    public void update(float mTemperatrue, float mPressure, float mHumidity) {
        // 接收氣象站的數(shù)據(jù)并展示
        this.mHumidity = mHumidity;
        this.mPressure = mPressure;
        this.mTemperatrue = mTemperatrue;
        display();
    }
    public void display() {
        System.out.println("***Today mTemperatrue:" + mTemperatrue + "***");
        System.out.println("***Today mPressure:" + mPressure + "***");
        System.out.println("***Today mHumidity:" + mHumidity + "***");
    }
}

public class ForcastConditions implements Observer{
    private float mTemperatrue;
    private float mPressure;
    private float mHumidity;
    @Override
    public void update(float mTemperatrue, float mPressure, float mHumidity) {
        this.mTemperatrue=mTemperatrue;
        this.mPressure=mPressure;
        this.mHumidity=mHumidity;
        display();
    }
    public void display(){
        System.out.println("**明天溫度:"+(mTemperatrue+Math.random())+"**");
        System.out.println("**明天氣壓:"+(mPressure+10*Math.random())+"**");
        System.out.println("**明天濕度:"+(mHumidity+Math.random())+"**");
    }
}
//使用方式
public class InternetWeather {
    public static void main(String[] args) {
        CurrentConditions mCurrentConditions;
        ForcastConditions mForcastConditions;
        WeatherDataSt mWeatherDataSt;
        mWeatherDataSt=new WeatherDataSt();
        mCurrentConditions=new CurrentConditions();
        mForcastConditions=new ForcastConditions();
        //將觀(guān)察者注冊(cè)到被觀(guān)察者的容器中
    mWeatherDataSt.registerObserver(mCurrentConditions);
    mWeatherDataSt.registerObserver(mForcastConditions); 
            //模擬產(chǎn)生數(shù)據(jù)
        mWeatherDataSt.setData(30, 150, 40);
        //撤銷(xiāo)觀(guān)察
    mWeatherDataSt.removeObserver(mCurrentConditions);
        mWeatherDataSt.setData(40, 250, 50);
    }
}
通過(guò)這種設(shè)計(jì)，將對(duì)天氣感興趣的公告板分離出來(lái)怔匣，自由擴(kuò)展握联，這樣氣象站內(nèi)部就不用維護(hù)各種公告板，可以作為一個(gè)獨(dú)立的服務(wù)運(yùn)行每瞒。
松耦合金闽，高內(nèi)聚，隔離影響