Java怎么实现简易购物系统

用基本语句去实现一个购物系统

package cn.ybk;
 
import java.util.Scanner;
 
/**
 * 简易的购物系统
 *
 * 1.主界面（选择）
 * 2.用户登录界面（验证用户信息）
 * 3.登录成功进入购物界面（商品选择）
 *
 */
public class ShoppingSystem {
 
    public static void main(String[] args) {
        String choose3;
        do {
            Scanner input = new Scanner(System.in);
            //1.主界面
            System.out.println("======================");
            System.out.println("========1.登录========");
            System.out.println("========2.退出========");
            System.out.println("======================");
            System.out.println("请输入选项（1   or  2）");
            int choose1 = input.nextInt();
            if (choose1 == 1) {
                //进入登录界面
                System.out.println("======请登录======");
                System.out.println("请输入用户名：");//输入用户名
                String username = input.next();
                System.out.println("请输入密码：");//输入密码
                String password = input.next();
 
 
                //登录成功
                if ("yangbenkun".equals(username) && "123456".equals(password)) {
                    System.out.println("欢迎用户：" + username);
                    System.out.println("->进入购物系统");
                    //打印商品菜单
                    System.out.println("商品编号\t商品名称\t\t\t商品单价");
                    System.out.println("1\t\t\tJava基础语法\t\t35.4");
                    System.out.println("2\t\t\tJava面向对象\t\t87");
                    System.out.println("3\t\t\tJava实战项目\t\t76");
 
                    double money1=0;//1的购物车单价
                    double money2 = 0;//2的购物车单价
                    double money3 =0;//3的购物车单价
                    double money = 0;//总金额
 
 
                    //do...while循环实现先多次购买
                    String choose2;
                    do {
                        System.out.println("请输入你要购买的商品编号：");
                        int no = input.nextInt();
                        if(no == 1){
                            System.out.println("请输入你要购买的数量：");
                            int sum1 = input.nextInt();
                            money1 = 35.4;
                            money1 *= sum1;
                            System.out.println("1的金额为："+money1);
 
                        }else if(no == 2){
                            System.out.println("请输入你要购买的数量：");
                            int sum2 = input.nextInt();
                            money2 = 87.0;
                            money2 *= sum2;
                            System.out.println("2的金额为："+money2);
 
                        }else if(no == 3){
                            System.out.println("请输入你要购买的数量：");
                            int sum3 = input.nextInt();
                            money3 = 76.0;
                            money3 *= sum3;
                            System.out.println("3的金额为："+money3);
                        }else {
                            System.out.println("选择有误请重新输入");
                        }
                        //计算总体金额
                         money = money1 + money2 + money3;
                        System.out.println("总金额为："+money);
                        System.out.println("是否继续购买(n/y)");
                         choose2 = input.next();
                    }while("y".equals(choose2));
 
                        if(money>=300){
                        System.out.println("总金额已经满300打七五折");
                        money*=0.75;
                    }
                    int i;//控制循环的循环变量的
                    do {
                        System.out.println("请输入你的余额");
                        double usermoney = input.nextDouble();
                        i = 1;
                        if (usermoney
这里只列举了些许商品和一些其他的东西，可以继续改进完善把功能做的更加详细。
程序运行截图：