小谈设计模式（15）—观察者模式

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

// 定义被观察者接口
interface Subject {
    void registerObserver(Observer observer);
    void removeObserver(Observer observer);
    void notifyObservers(String message);
}

// 具体观察者类
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);
    }
}

// 具体被观察者类
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 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.notifyObservers("Hello, observers!");

        subject.removeObserver(observer2);

        subject.notifyObservers("Observer 2 has been removed!");

    }
}

Observer 1 received message: Hello, observers!
Observer 2 received message: Hello, observers!
Observer 1 received message: Observer 2 has been removed!