【设计模式】用Java实现观察者模式

import java.util.ArrayList;
import java.util.List;
// 主题 - 被观察者
interface Subject {
    void registerObserver(Observer observer);
    void removeObserver(Observer observer);
    void notifyObservers();
}
// 具体主题 - 商品
class Product implements Subject {
    private List<Observer> observers;
    private String name;
    public Product(String name) {
        this.observers = new ArrayList<>();
        this.name = name;
    }
    public void setName(String name) {
        this.name = name;
        notifyObservers();
    }
    public String getName() {
        return name;
    }
    public void registerObserver(Observer observer) {
        observers.add(observer);
    }
    public void removeObserver(Observer observer) {
        observers.remove(observer);
    }
    public void notifyObservers() {
        for (Observer observer : observers) {
            observer.update(this);
        }
    }
}
// 观察者
interface Observer {
    void update(Subject subject);
}
// 具体观察者 - 用户
class User implements Observer {
    private String name;
    public User(String name) {
        this.name = name;
    }
    public void update(Subject subject) {
        if (subject instanceof Product) {
            Product product = (Product) subject;
            System.out.println(name + " received a notification: " + product.getName() + " is now available.");
        }
    }
}
// 使用示例
public class Main {
    public static void main(String[] args) {
        // 创建主题对象
        Product product = new Product("iPhone 13");
        // 创建观察者对象
        User user1 = new User("John");
        User user2 = new User("Alice");
        // 注册观察者
        product.registerObserver(user1);
        product.registerObserver(user2);
        // 修改主题状态并通知观察者
        product.setName("iPhone 14");
    }
}