侦听helper类中的变量更改

// 主题接口
interface Subject {
    void registerObserver(Observer o);
    void removeObserver(Observer o);
    void notifyObservers();
}

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

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

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

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

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

    public void setMessage(String message) {
        this.message = message;
        notifyObservers();
    }
}

// 具体观察者
class ConcreteObserver implements Observer {
    private String name;

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

    @Override
    public void update(String message) {
        System.out.println(name + " received message: " + message);
    }
}

// 测试代码
public class ObserverPatternExample {
    public static void main(String[] args) {
        ConcreteSubject subject = new ConcreteSubject();
        Observer observer1 = new ConcreteObserver("Observer 1");
        Observer observer2 = new ConcreteObserver("Observer 2");

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

        subject.setMessage("Hello Observers!");
    }
}