Java自动售水系统

import java.util.*;

public class k28 {
public static void main(String[] args){
Scanner in=new Scanner(System.in);
System.out.println("\t自动售水系统【满20元享9折】");
System.out.println("=========================================");
System.out.println("1.矿泉水 2.咖啡 3.百事可乐 \n4.冰红茶 5.脉动 6.雪碧");
double price;
System.out.println("请输入购买的商品编号：");
int i=in.nextInt();
switch(i){
case 1:
price=2;break;
case 2:
price=5.5;break;
case 3:
price=3;break;
case 4:
price=3;break;
case 5:
price=4.5;break;
case 6:
price=2.5;break;
default:
System.out.println("该商品已下架！");
return;
}
System.out.println("请输入购买的数量：");
int num=in.nextInt();
double total=price*num;//应付金额
String s="";
if(total>=20){
total=total*0.9;
s="已享受9折优惠！";
}
System.out.println(s+"请付款"+total+"元！");
System.out.println("请输入付款金额：");
double fk=in.nextDouble();
if(fk<total){
System.out.println("付款金额不足");
System.out.println("******谢谢惠顾********");
return;
}
else if(fk==total){
System.out.println("金额已付，请取走商品！");
System.out.println("******谢谢惠顾********");
}
else if(fk>total){
String z=String.format("%2f",(fk-total));

System.out.println("找零：" +z+"元！");
System.out.println("金额已付，请取走商品！");
System.out.println("******谢谢惠顾********");
}
}

}