觀察者模式:
定義了一種一對多的依賴關係,讓多個觀察者對同一個對象進行監聽,當這個對象的狀態(值發生改變)發生改變時,會通知所有觀察者,讓其自己自動更新自己.
實現代碼:
1.定義要觀察的抽象對象(Watcher)-抽象被觀察者
public interface Watcher {
public void update(String str);
}
2.定義觀察者的抽象對象(Watched)-抽象觀察者
public interface Watched {
public void addWatcher(Watcher watcher);
public void removeWatcher(Watcher watcher);
public void notifyWatcher(String str);
}
3.具體的要觀察的對象(ConcreteWatcher)-實際被觀察者
public class ConcreteWatcher implements Watcher{
@Override
public void update(String str) {
System.out.println(str);
}
}
4.具體的觀察者對象(ConcreateWatched)-實際的觀察者
public class ConcreateWatched implements Watched {
// 存放觀察者
private List<Watcher> list = new ArrayList<Watcher>();
@Override
public void addWatcher(Watcher watcher) {
list.add(watcher);
}
@Override
public void removeWatcher(Watcher watcher) {
list.remove(watcher);
}
@Override
public void notifyWatcher(String str) {
for (Watcher watcher : list)
{
watcher.update(str);
}
}
}
5.建立測試類
public class Test {
public static void main(String[] args) {
Watched girl = new ConcreateWatched();
Watcher watcher1 = new ConcreteWatcher();
Watcher watcher2 = new ConcreteWatcher();
Watcher watcher3 = new ConcreteWatcher();
girl.addWatcher(watcher1);
girl.addWatcher(watcher2);
girl.addWatcher(watcher3);
girl.notifyWatcher("開心");
girl.notifyWatcher("hello world");
}
}
最後運行的結果:
開心
開心
開心
hello world
hello world
hello world