觀察者模式

GoF設計模式裏面的觀察者模式的UML圖

PS：發佈和訂閱（事件監聽，mq，多路IO複用）
例如：XX樓盤5-1開盤，你肯定不知道，如果你想知道，肯定要去樓盤登記，留下電話號5-1號銷售就會打電話通知你。

Subject 就是抽象主題：它負責管理所有觀察者的引用，同時定義主要的事件操作。
ConcreteSubject 具體主題：它實現了抽象主題的所有定義的接口，當自己發生變化時，會通知所有觀察者。
Observer 觀察者：監聽主題發生變化相應的操作接口。

代碼案例

public class EventObject implements Serializable {

    private String type;
    private Object data;

    public EventObject(String type, Object data) {
        this.type = type;
        this.data = data;
    }

    public String getType() {
        return type;
    }

    public Object getData() {
        return data;
    }
}

//subject
public interface Lifecycle {

    public void addLifecycleListener(LifecycleListener listener);

    public void removeLifecycleListener(LifecycleListener listener);

    public void fireLifecycleEvent(String type,Object data);
}

//ConcreteSubject 
public class LifecycleSubject implements Lifecycle {

    private CopyOnWriteArrayList<LifecycleListener> cwal = new CopyOnWriteArrayList();

    @Override
    public void addLifecycleListener(LifecycleListener listener) {
        cwal.add(listener);
    }

    @Override
    public void removeLifecycleListener(LifecycleListener listener) {
        cwal.remove(listener);
    }

    @Override
    public void fireLifecycleEvent(String type, Object data) {

        EventObject event = new EventObject(type, data);
        for (int i = 0; i < cwal.size(); i++) {
            cwal.get(i).lifecycleEvent(event);
        }

    }
}

//觀察者行爲
public interface LifecycleListener {
    public void lifecycleEvent(EventObject event);
}

//具體的觀察者
public class ObserverSubject implements LifecycleListener {

    @Override
    public void lifecycleEvent(EventObject event) {
        System.out.println(event.getType() + "=" + event.getData());
    }
}

public class Client {
    public static void main(String[] args) {
        LifecycleSubject lifecycleSubject = new LifecycleSubject();
        lifecycleSubject.addLifecycleListener(new ObserverSubject());
        lifecycleSubject.fireLifecycleEvent("start", "how are you");
    }
}