零钱通（java）面向过程

package com.Wzg;

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

public class Smallchange {
    public static void main(String[] args) {
        System.out.println("============零钱通菜单============");
        System.out.println("ttt1   零钱通明细");
        System.out.println("ttt2   收益入账");
        System.out.println("ttt3   消费");
        System.out.println("ttt4   退出");
        boolean loop=true;
        Scanner scanner= new Scanner(System.in);
        String a1="          ---------零钱通明细---------";
        double money=0;
        double balance=0;
        String b1="";
        Date date=new Date();//获取当前系统的时间，国外格式
        SimpleDateFormat sim=new SimpleDateFormat("yyyy-MM-dd HH:mm");//将时间转换为我们的格式
        do {
            System.out.print("请选择:");
            int a=scanner.nextInt();
            switch (a){
                case 1:
                    System.out.println("   "+a1);
                    break;
                case 2:
                    System.out.print("请输入入账金额：");
                    money=scanner.nextDouble();
                    if(money<=0){
                        System.out.println("输入有误，请重新输入!");
                        break;
                    }
                    balance+=money;
                    a1+="n   "+"收益入账"+"t"+"+"+money+"t"+sim.format(date)+"t"+"余额:"+balance;
                    System.out.println("收益入账"+"t"+"+"+money+"t"+sim.format(date)+"t"+"余额:"+balance);
                    break;
                case 3:
                    System.out.print("请输入消费金额：");
                    money=scanner.nextDouble();
                    balance-=money;
                    if(money>balance){
                        System.out.println("输入有误，请重新输入!");
                        break;
                    }
                    System.out.print("请输入消费说明：");
                    b1=scanner.next();
                    a1+="n   "+b1+"t"+"    -"+money+"t"+sim.format(date)+"t"+"余额:"+balance;
                    break;
                case 4:
                    System.out.print("是否确认退出(y/n)：");
                    b1=scanner.next();
                    while (true){
                        if(b1.equals("y")||b1.equals("n")){
                            break;
                        }
                    }
                    if(b1.equals("y")){
                        loop=false;
                    }
                    break;
                default:
                    System.out.println("选择有误!");
            }

        }while (loop);
        System.out.print("程序结束");
    }
}