零钱通（面向过程）完整版

package com.hspedu.smallchange;

import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Scanner;

public class SmallChangeSys {
    public static void main(String[] args) {
        //零钱通明细
        String key;
        boolean x = true;
        String detail = "-------------零钱通明细-------------";
        double money = 0;
        double balance = 0;
        Date date = null;
        String exit;
        SimpleDateFormat sdf = new SimpleDateFormat("YYYY-MM-dd HH:mm");
        //消费类型，就是你买了什么
        String note;
        do {
            Scanner sc = new Scanner(System.in);
            System.out.println("\n=============零钱通菜单=============");
            System.out.println("\t\t\t1 零钱通明细");
            System.out.println("\t\t\t2 收益入账");
            System.out.println("\t\t\t3 消费");
            System.out.println("\t\t\t4 退出");
            System.out.print("请输入(1-4):");
            key = sc.next();
            switch (key) {
                case "1":
                    System.out.println(detail);
                    break;
                case "2":

                    //判断输入的金额是否合理
                   /* if(money <= 0){
                        System.out.println("\n入账的金额应该大于0");
                        break;
                    }*/
                    while (true) {
                        System.out.print("\n您本次收益入账金额是多少？");
                        money = sc.nextDouble();
                        if (money <= 0) {
                            System.out.println("\n入账的金额应该大于0\n");
                        } else {
                            System.out.println("\n本次入账" + money + "元\n");
                            break;
                        }
                    }
                    balance += money;
                    date = new Date();
                    detail += "\n收益入账\t+" + money + "\t" + sdf.format(date) + "\t" + balance;
                    break;
                case "3":

                    while (true) {
                        System.out.print("您本次消费多少钱？");
                        money = sc.nextDouble();
                        if (money <= 0) {
                            System.out.println("\n消费的金额应该大于0\n");
                            break;
                        } else {
                            break;
                        }
                    }
                    if (money >= balance) {
                        System.out.println("\n余额不够，你还有" + balance + "元。你怎么花？\n");
                        break;
                    }
                    balance -= money;
                    System.out.print("您消费了什么商品？");
                    note = sc.next();
                    date = new Date();
                    detail += "\n" + note + "\t-" + money + "\t" + sdf.format(date) + "\t" + balance;
                    System.out.println("\n本次消费购买了" + note + "\t花费了" + money);
                    break;
                case "4":
                    while (true) {
                        System.out.println("你确定要退出吗？输入y/n");
                        exit = sc.next();
                        if (exit.equals("y") || exit.equals("n")) {
                            break;//这里是判断用户输入了是不是y或n，如果是就退出while循环；一块代码实现一个功能;巧妙点在于
                            //如果输入了n就break，重新进入do循环，也就是又开始显示菜单
                        } else {
                            System.out.println("指令输入有误，输入y或者n");
                        }
                    }
                    if (exit.equals("y")) {
                        x = false;//这里判断输入的是y的话，就把x改为false，在倒数第二个代码上就实现了退出系统了
                        break;
                    }
                    break;
                default:
                    System.out.println("你的输入有误，请重新输入");
            }
        } while (x);
        System.out.println("退出了零钱通项目");
    }
}