如何在可观察对象发生更改时发布通知

// 定义观察者接口
interface Observer {
    void update();
}

// 定义可观察对象接口
interface Observable {
    void addObserver(Observer observer);
    void removeObserver(Observer observer);
    void notifyObservers();
}

// 具体的可观察对象类
class ConcreteObservable implements Observable {
    private List<Observer> observers = new ArrayList<>();
    private int state;

    public void setState(int state) {
        this.state = state;
        notifyObservers();
    }

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

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

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

// 具体的观察者类
class ConcreteObserver implements Observer {
    private String name;
    private ConcreteObservable observable;

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

    @Override
    public void update() {
        System.out.println(name + " received notification. New state: " + observable.getState());
    }
}

// 示例代码
public class Main {
    public static void main(String[] args) {
        ConcreteObservable observable = new ConcreteObservable();
        ConcreteObserver observer1 = new ConcreteObserver("Observer 1", observable);
        ConcreteObserver observer2 = new ConcreteObserver("Observer 2", observable);

        observable.addObserver(observer1);
        observable.addObserver(observer2);

        observable.setState(1);
        observable.setState(2);

        observable.removeObserver(observer2);

        observable.setState(3);
    }
}