Features Required:

User Registration and Authentication: Users should be able to create accounts, log in, and authenticate themselves to access the food ordering and delivery system.
Restaurant Listings: The system should provide a list of restaurants with details such as name, cuisine, ratings, and availability.
Menu and Item Selection: Users should be able to view menus, select items, customize options, and add them to their cart for ordering.
Cart Management: Users should be able to manage their cart by adding or removing items, adjusting quantities, and applying discounts or offers.
Order Placement: Users should be able to place orders, specify delivery addresses, and choose payment methods.
Order Tracking: Users should be able to track the status of their orders, including real-time updates on preparation, packaging, and delivery.
Delivery Management: The system should handle the assignment of delivery personnel, route optimization, and estimated delivery times.
Reviews and Ratings: Users should be able to rate and provide reviews for restaurants and their ordered items.

Design Patterns Involved or Used:

Model-View-Controller (MVC) Pattern: The MVC pattern can be used to separate the application into three components: the model (data and business logic), the view (user interface), and the controller (handles user interactions and manages the flow of data).
Singleton Pattern: The Singleton pattern can be used to ensure that only one instance of certain classes, such as the user authentication manager or the order manager, is created and shared across the system.
Factory Pattern: The Factory pattern can be used to create different types of objects, such as users, restaurants, or menu items, based on user requests.
Observer Pattern: The Observer pattern can be used to notify users about changes in order status, such as updates on preparation, packaging, or delivery.
Decorator Pattern: The Decorator pattern can be used to add additional functionality or features, such as discounts, offers, or user preferences, to the core classes in the system.
Proxy Pattern: The Proxy pattern can be used to handle the communication between clients and the actual restaurant or delivery service, providing a level of indirection and encapsulation for network operations.

Code: Classes Detailed Implementation Based on Patterns Mentioned Above

// User class
class User {
    private String userId;
    private String username;
    private String password;
    // Other attributes and methods

    public User(String userId, String username, String password) {
        this.userId = userId;
        this.username = username;
        this.password = password;
    }

    // Getters and setters
}

// Restaurant class
class Restaurant {
    private String restaurantId;
    private String name;
    private String cuisine;
    private double rating;
    // Other attributes and methods

    public Restaurant(String restaurantId, String name, String cuisine, double rating) {
        this.restaurantId = restaurantId;
        this.name = name;
        this.cuisine = cuisine;
        this.rating = rating;
    }

    // Getters and setters
}

// MenuItem class
class MenuItem {
    private String itemId;
    private String name;
    private double price;
    // Other attributes and methods

    public MenuItem(String itemId, String name, double price) {
        this.itemId = itemId;
        this.name = name;
        this.price = price;
    }

    // Getters and setters
}

// CartItem class
class CartItem {
    private MenuItem menuItem;
    private int quantity;
    // Other attributes and methods

    public CartItem(MenuItem menuItem, int quantity) {
        this.menuItem = menuItem;
        this.quantity = quantity;
    }

    // Getters and setters
}

// Order class
class Order {
    private String orderId;
    private User user;
    private List<CartItem> cartItems;
    private String deliveryAddress;
    private String paymentMethod;
    // Other attributes and methods

    public Order(String orderId, User user, List<CartItem> cartItems, String deliveryAddress, String paymentMethod) {
        this.orderId = orderId;
        this.user = user;
        this.cartItems = cartItems;
        this.deliveryAddress = deliveryAddress;
        this.paymentMethod = paymentMethod;
    }

    // Getters and setters
}

// Observer interface
interface OrderObserver {
    void update(Order order);
}

// OrderStatusTracker class
class OrderStatusTracker implements OrderObserver {
    private User user;

    public OrderStatusTracker(User user) {
        this.user = user;
    }

    @Override
    public void update(Order order) {
        // Update order status for the user
        System.out.println("Order status updated for user " + user.getUsername() + ": " + order.getStatus());
    }
}

// Main Class
public class FoodOrderingSystem {
    public static void main(String[] args) {
        // Create users
        User user1 = new User("user1", "John", "password1");
        User user2 = new User("user2", "Alice", "password2");

        // Create restaurants
        Restaurant restaurant1 = new Restaurant("restaurant1", "Restaurant 1", "Italian", 4.5);
        Restaurant restaurant2 = new Restaurant("restaurant2", "Restaurant 2", "Indian", 4.2);

        // Create menu items
        MenuItem item1 = new MenuItem("item1", "Pizza", 10.99);
        MenuItem item2 = new MenuItem("item2", "Pasta", 8.99);

        // Create cart items
        CartItem cartItem1 = new CartItem(item1, 2);
        CartItem cartItem2 = new CartItem(item2, 1);

        // Create orders
        Order order1 = new Order("order1", user1, Arrays.asList(cartItem1, cartItem2), "123 Street, City", "Credit Card");
        Order order2 = new Order("order2", user2, Arrays.asList(cartItem1), "456 Street, City", "PayPal");

        // Subscribe order status tracker to orders
        OrderStatusTracker statusTracker1 = new OrderStatusTracker(user1);
        OrderStatusTracker statusTracker2 = new OrderStatusTracker(user2);

        order1.subscribeObserver(statusTracker1);
        order2.subscribeObserver(statusTracker2);

        // Update order status
        order1.updateStatus("Preparing");
        order2.updateStatus("Out for Delivery");
    }
}

In this code example, the User class represents a user of the food ordering system, the Restaurant class represents a restaurant with its details, the MenuItem class represents an item on the restaurant's menu, the CartItem class represents an item added to the user's cart, and the Order class represents a placed order.

The code demonstrates the usage of classes based on the mentioned patterns, such as the Observer pattern for tracking and updating the order status for users, the Singleton pattern (not explicitly shown in the code) for creating a single instance of the user authentication manager or the order manager, the Factory pattern for creating different objects based on user requests, the Decorator pattern (not explicitly shown in the code) for adding discounts or offers to the core classes, and the Proxy pattern (not explicitly shown in the code) for handling communication between clients and the actual restaurant or delivery service.

Please note that this is a simplified example, and a complete implementation of an online food ordering and delivery system involves more complex components, such as user authentication and authorization, payment processing, location-based services, real-time order tracking, and integration with external services for restaurant and delivery management.

Design (LLD) a system for online food ordering and delivery like Zomato - Machine Coding