如何实现观察者模式的update方法

// 观察者接口
public interface Observer {
    void update(String message);
}

// 主题接口
public interface Subject {
    void registerObserver(Observer observer);
    void removeObserver(Observer observer);
    void notifyObservers(String message);
}

// 具体观察者类
public class ConcreteObserver implements Observer {
    @Override
    public void update(String message) {
        // 处理通知消息
        System.out.println("收到通知：" + message);
    }
}

// 具体主题类
public class ConcreteSubject implements Subject {
    private List<Observer> observers = new ArrayList<>();

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

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

    @Override
    public void notifyObservers(String message) {
        for (Observer observer : observers) {
            observer.update(message);
        }
    }
}

// 测试代码
public class ObserverPatternTest {
    public static void main(String[] args) {
        ConcreteSubject subject = new ConcreteSubject();
        ConcreteObserver observer1 = new ConcreteObserver();
        ConcreteObserver observer2 = new ConcreteObserver();

        subject.registerObserver(observer1);
        subject.registerObserver(observer2);

        subject.notifyObservers("Hello, observers!");

        subject.removeObserver(observer2);

        subject.notifyObservers("Observer2 has been removed.");
    }
}