觀察者模式定義：對象之間多對一依賴的一種設計方案，被依賴的對象爲Subject，依賴的對象爲Observer，Subject通知Oberver變化。
觀察者模式就像小時候的訂牛奶業務
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奶站：相當於Subject，負責訂奶家庭的登記，派送，退訂工作
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用戶：相當於Oberver，訂奶家庭
Subject：負責用戶的登記註冊，移除和通知
Oberver：負責接收Subject的通知輸入
代碼案例：
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//觀察者public interface Observer
{ public void update();} |
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public class MilkFamily implements Observer
{ private String
familyName; public MilkFamily(String
familyName) { this.familyName
= familyName; } @Override public void update()
{ System.out.println(familyName+"--------收到牛奶"); }} |
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//被觀察者public abstract class Observable
{ protected List<Observer>
observerList = new ArrayList<Observer>(); //添加觀察者 public void addObserver(Observer
observer){ observerList.add(observer); } //移除觀察者 public void deleteObserver(Observer
observer){ observerList.remove(observer); } //通知所有觀察者 public void notifyObservers(){ for(Observer
o : observerList){ o.update(); } } } |
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public class MileStation extends Observable
{ public void deliver(){ System.out.println("新的一天到了，牛奶站準備送牛奶了。。。。。。"); super.notifyObservers(); }} |
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public class Main
{ public static void main(String
args[]){ MileStation
mileStation = new MileStation(); MilkFamily
milkFamily = new MilkFamily("小小巫的家"); MilkFamily
milkFamily2 = new MilkFamily("巫巫巫的家"); mileStation.addObserver(milkFamily); mileStation.addObserver(milkFamily2); mileStation.deliver(); }} |
