1.觀察者定義了一種一對多依賴關系，讓多個觀察者同時監聽某個主題對象。這個主題對象在狀態上發生變化時，會通知所有的觀者對象，讓他們自動更新自己。----這里的主題對象就是被觀察者

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2.代碼模擬

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?? 抽象主題角色AbstractWatched.java

???public interface AbstractWatched {

Java代碼? ?

????public?void?addWatcher(AbstractWatcher?watcher);??

??????

????public?void?removeWatcher(AbstractWatcher?watcher);??

??????

????public?void?removeAll();??

??????

????public?void?fire();??

}??

?? ? ?具體主題角色ConcreteWatched.java

???public class ConcreteWatched implements AbstractWatched {

Java代碼? ?

private?List<AbstractWatcher>?watchers?=?new?ArrayList<AbstractWatcher>();??

??

@Override??

public?void?addWatcher(AbstractWatcher?watcher)?{??

????watchers.add(watcher);??

}??

??

@Override??

public?void?removeAll()?{??

????watchers.clear();??

}??

??

@Override??

public?void?removeWatcher(AbstractWatcher?watcher)?{??

????watchers.remove(watcher);??

}??

??

@Override??

public?void?fire()?{??

??????

????for(AbstractWatcher?watcher?:?watchers){??

????????watcher.update();??

????}??

}??

?

?? 抽象觀察者角色

???public interface AbstractWatcher {

Java代碼? ?

public?void?update();??

???

???

?

?? 具體觀者角色

?

Java代碼? ?

public?class?ConcreteWatcher?implements?AbstractWatcher?{??

??

????@Override??

????public?void?update()?{??

????????System.out.println("update.....");??

????}??

??

}??

?

??測試代碼：

?

Java代碼? ?

public?static?void?main(String[]?args)?{??

????//被觀察者??

????AbstractWatched?watched?=?new?ConcreteWatched();??

??????

????AbstractWatcher?watcher1?=?new?ConcreteWatcher();??

????AbstractWatcher?watcher2?=?new?ConcreteWatcher();??

????AbstractWatcher?watcher3?=?new?ConcreteWatcher();??

??????

????watched.addWatcher(watcher1);??

????watched.addWatcher(watcher2);??

????watched.addWatcher(watcher3);??

??????

????watched.fire();??

} ?

轉載于:https://my.oschina.net/wdkxyd/blog/160415

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