设计模式之观察者模式

/**
 * 抽象主题角色
 */
public interface Topic {
    /**
     * 观察者注册
     * @param observer
     */
    void registerObserver(Observer observer);

    /**
     * 删除观察者
     * @param observer
     */
    void removeObserver(Observer observer);

    /**
     * 通知观察者
     */
    void notifyObservers();

    /**
     * 主题状态变化
     * @param msg
     */
    void msgChange(String msg);
}

public class TopicImpl implements  Topic{
    private List<Observer> observerList = new ArrayList<Observer>();
    private String msg ;

    @Override
    public void registerObserver(Observer observer) {
        this.observerList.add(observer);
    }

    @Override
    public void removeObserver(Observer observer) {
        this.observerList.remove(observer);
    }

    @Override
    public void notifyObservers() {
        for(Observer observer : observerList){
            observer.update(msg);
        }
    }

    @Override
    public void msgChange(String msg) {
        this.msg = msg;
    }
}

/**
 * 抽象观察者
 */
public interface Observer {
    /**
     * 观察者收到信息做处理
     * @param msg
     */
    void update(String msg);
}

/**
 * 观察者1
 */
public class ObserverImpl implements Observer{
    @Override
    public void update(String msg) {
        System.out.println("ObserverImpl receive msg :" + msg);
    }
}

/**
 * 观察者2
 */
public class ObserverImpl2 implements Observer{
    @Override
    public void update(String msg) {
        System.out.println("ObserverImpl2 receive msg:" + msg);
    }
}

/**
 * 测试类
 */
public class MainTest {
    public static void main(String[] args) {
        Topic topic = new TopicImpl();

        Observer observer1 = new ObserverImpl();
        Observer observer2 = new ObserverImpl2();

        topic.registerObserver(observer1);
        topic.registerObserver(observer2);

        topic.msgChange("Java 是面向对象的语言");
        topic.notifyObservers();
    }
}

4、运行结果