软件设计中使用观察者模式实现订餐管理系统

订餐管理系统可以使用观察者模式来实现订单状态更新的通知。以下是一个示例：

1. 定义观察者接口

public interface Observer {
    void update(Order order);
}

2. 定义主题接口

public interface Subject {
    void attach(Observer observer);
    void detach(Observer observer);
    void notifyObservers(Order order);
}

3. 实现主题接口

public class OrderManager implements Subject {
    private List<Observer> observers;
    private List<Order> orders;

    public OrderManager() {
        this.observers = new ArrayList<>();
        this.orders = new ArrayList<>();
    }

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

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

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

    public void addOrder(Order order) {
        orders.add(order);
        notifyObservers(order);
    }

    public void updateOrderStatus(int orderId, OrderStatus status) {
        for (Order order : orders) {
            if (order.getId() == orderId) {
                order.setStatus(status);
                notifyObservers(order);
                break;
            }
        }
    }
}

4. 实现观察者接口

public class OrderNotification implements Observer {
    private String name;

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

    @Override
    public void update(Order order) {
        System.out.println(name + ": Order #" + order.getId() + " status updated to " + order.getStatus());
    }
}

5. 使用示例

OrderManager orderManager = new OrderManager();
Observer notification1 = new OrderNotification("User1");
Observer notification2 = new OrderNotification("User2");
orderManager.attach(notification1);
orderManager.attach(notification2);

Order order1 = new Order(1, "Pizza", OrderStatus.CREATED);
orderManager.addOrder(order1);

orderManager.updateOrderStatus(1, OrderStatus.PREPARING);

输出：

User1: Order #1 status updated to PREPARING
User2: Order #1 status updated to PREPARING

当有新订单添加或订单状态更新时，观察者会收到通知并进行相应处理。这样就可以实现订餐管理系统的订单状态更新通知功能。