用Java实现设计商品类（Product class），包括商品属性和方法，如商品名称、价格、库存数量、加入购物车、从购物车移除等； 设计购物车类（ShoppingCart class），包括购物车属性和方法，如购物车列表、添加商品、移除商品、结算等； 设计用户类（User class），包括用户属性和方法，如用户名、密码、购物车、订单记录等； 设计订单类（Order class），包括订单属性和方法，如订单号、订单时间、订单详情（即购买的商品信息）等； 实现以上类及其方法，并编写主函数，模拟用户使用场景，如浏览商品，添加到购物车，结算下单等。

好的，以下是Java实现的代码：

Product类：

public class Product {
    private String name;
    private double price;
    private int stock;

    public Product(String name, double price, int stock) {
        this.name = name;
        this.price = price;
        this.stock = stock;
    }

    public String getName() {
        return name;
    }

    public double getPrice() {
        return price;
    }

    public int getStock() {
        return stock;
    }

    public void setStock(int stock) {
        this.stock = stock;
    }

    public void addToCart(ShoppingCart cart) {
        cart.addProduct(this);
    }

    public void removeFromCart(ShoppingCart cart) {
        cart.removeProduct(this);
    }
}

ShoppingCart类：

import java.util.ArrayList;
import java.util.List;

public class ShoppingCart {
    private List<Product> productList = new ArrayList<>();

    public void addProduct(Product product) {
        if (product.getStock() > 0) {
            productList.add(product);
            product.setStock(product.getStock() - 1);
        } else {
            System.out.println("商品库存不足！");
        }
    }

    public void removeProduct(Product product) {
        productList.remove(product);
        product.setStock(product.getStock() + 1);
    }

    public double getTotalPrice() {
        double total = 0;
        for (Product product : productList) {
            total += product.getPrice();
        }
        return total;
    }

    public void checkout(User user) {
        if (user.getShoppingCart() == this) {
            if (user.getBalance() >= getTotalPrice()) {
                Order order = new Order(user, productList);
                user.addOrder(order);
                user.setBalance(user.getBalance() - getTotalPrice());
                productList.clear();
                System.out.println("下单成功！");
            } else {
                System.out.println("余额不足！");
            }
        } else {
            System.out.println("购物车与用户不匹配！");
        }
    }
}

User类：

import java.util.ArrayList;
import java.util.List;

public class User {
    private String username;
    private String password;
    private double balance;
    private ShoppingCart shoppingCart = new ShoppingCart();
    private List<Order> orderList = new ArrayList<>();

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

    public String getUsername() {
        return username;
    }

    public String getPassword() {
        return password;
    }

    public double getBalance() {
        return balance;
    }

    public void setBalance(double balance) {
        this.balance = balance;
    }

    public ShoppingCart getShoppingCart() {
        return shoppingCart;
    }

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

Order类：

import java.util.List;

public class Order {
    private static int orderCount = 0;
    private int orderId;
    private User user;
    private List<Product> productList;

    public Order(User user, List<Product> productList) {
        this.orderId = ++orderCount;
        this.user = user;
        this.productList = productList;
    }

    public int getOrderId() {
        return orderId;
    }

    public User getUser() {
        return user;
    }

    public List<Product> getProductList() {
        return productList;
    }
}

主函数：

public class Main {
    public static void main(String[] args) {
        // 创建商品
        Product product1 = new Product("商品1", 10, 5);
        Product product2 = new Product("商品2", 20, 3);
        Product product3 = new Product("商品3", 30, 2);

        // 创建用户
        User user1 = new User("用户1", "123456", 100);

        // 用户1浏览商品
        System.out.println("用户1正在浏览商品...");
        System.out.println("商品名称\t商品价格\t商品库存");
        System.out.println(product1.getName() + "\t" + product1.getPrice() + "\t" + product1.getStock());
        System.out.println(product2.getName() + "\t" + product2.getPrice() + "\t" + product2.getStock());
        System.out.println(product3.getName() + "\t" + product3.getPrice() + "\t" + product3.getStock());

        // 用户1将商品1和商品2加入购物车
        System.out.println("用户1将商品1和商品2加入购物车...");
        product1.addToCart(user1.getShoppingCart());
        product2.addToCart(user1.getShoppingCart());

        // 用户1查看购物车并结算
        System.out.println("用户1查看购物车并结算...");
        System.out.println("购物车商品列表：");
        for (Product product : user1.getShoppingCart().getProductList()) {
            System.out.println(product.getName() + "\t" + product.getPrice());
        }
        System.out.println("总价：" + user1.getShoppingCart().getTotalPrice());
        user1.getShoppingCart().checkout(user1);

        // 用户1查看订单记录
        System.out.println("用户1查看订单记录...");
        System.out.println("订单号\t订单时间\t\t订单详情");
        for (Order order : user1.getOrderList()) {
            System.out.print(order.getOrderId() + "\t" + "2021-01-01 00:00:00" + "\t");
            for (Product product : order.getProductList()) {
                System.out.print(product.getName() + "\t");
            }
            System.out.println();
        }
    }
}