观察者模式

public interface Observer {
    void accept(String message);
}

public class ConcreteObserver implements Observer {
    String name;

    public ConcreteObserver(String name) {
        this.name = name;
    }

    @Override
    public void accept(String message) {
        System.out.println("观察者：" + name + "接收消息：" + message);
    }
}

public interface BeiObserver {
    void add(Observer observer);

    void del(Observer observer);

    void send(String message);

}

public class ConcreteBeiObserver implements BeiObserver {
    ArrayList<Observer> list = new ArrayList<>();

    public ConcreteBeiObserver() {
    }

    public ConcreteBeiObserver(ArrayList<Observer> list) {
        this.list = list;
    }

    @Override
    public void add(Observer observer) {
        list.add(observer);
    }

    @Override
    public void del(Observer observer) {
        list.remove(observer);
    }

    @Override
    public void send(String message) {
        for (Observer observer : list) {
            observer.accept(message);
        }
    }
}

测试

public class Test {
    public static void main(String[] args) {
        ConcreteObserver observer1 = new ConcreteObserver("周杰伦");
        ConcreteObserver observer2 = new ConcreteObserver("周杰");
        ConcreteBeiObserver concreteBeiObserver = new ConcreteBeiObserver();
        concreteBeiObserver.add(observer1);
        concreteBeiObserver.add(observer2);
        concreteBeiObserver.send("更新");
    }
}