这算是实现了观察者模式吗？

Question

public interface Observer {
    // 监听
    public void update(String msg);
}
public class ObserverImpl implements Observer {


    @Override
    public void update(String msg) {
        System.out.println("观察者发现消息："+msg);
    }
}
public interface Subject {
    /**
     *增加观察者
     */
    public void add(Observer observerVo);
    /**
     *删除观察者
     */
    public void delete(Observer observerVo);
    /**
     *发送观察者消息
     */
    public void notifyObservers(String msg);
}
public class SubjectImpl implements Subject {

    private List<Observer> observerVoList = new ArrayList<>();

    /**
     * 增加观察者
     *
     * @param observerVo
     */
    @Override
    public void add(Observer observerVo) {
        observerVoList.add(observerVo);
    }

    /**
     * 删除观察者
     *
     * @param observerVo
     */
    @Override
    public void delete(Observer observerVo) {
        observerVoList.remove(observerVo);
    }

    /**
     * 发送观察者消息
     *
     * @param msg
     */
    @Override
    public void notifyObservers(String msg) {
        if (observerVoList != null && observerVoList.size()>0){
            for (Observer observerVo: observerVoList){
                observerVo.update(msg);
            }
        }
    }
}
public class ObserverTest {
    @Test
    public void test(){
        Subject subject = new SubjectImpl();
        subject.add(new ObserverImpl());
        subject.add(new ObserverImpl());
        subject.add(new ObserverImpl());
        subject.notifyObservers("更新");
    }
}