ackage cn.practice1200;
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import java.util.Scanner;
public class Eater_Alliance {
/**
* 吃货联盟订餐系统
*
* @author QCD
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
Scanner input = new Scanner(System.in);
// 初始化3个数组存储菜品、价格、点赞数
String[] dishNames = { "苦瓜炒鸡蛋", "红烧排骨", "辣子鸡丁", "石锅鱼", "麻婆豆腐" };
double[] prices = { 15.0, 30.0, 35.0, 90.0, 20.0 };
int[] praiseNums = new int[5];
// 在初始化6个数组用于存储订单信息
String[] names = new String[5];// 保存订餐人姓名
String[] dishMegs = new String[5];// 保存所选菜品名
int[] dishNums = new int[5];// 保存所选菜品份数
int[] times = new int[5];// 保存送餐时间
String[] addresses = new String[5];// 保存送餐地址
int[] states = new int[5];// 保存订单状态：0表示已预订，1表示已完成
double[] sumPrices = new double[5];// 保存订单的总金额
// 初始化2条订单信息
// 第1条
names[0] = "王大锤";
dishMegs[0] = "辣子鸡丁";
dishNums[0] = 2;
times[0] = 12;
addresses[0] = "莞太路3号";
states[0] = 0;
sumPrices[0] = 70.0;
// 第2条
names[1] = "王大柱";
dishMegs[1] = "麻婆豆腐";
dishNums[1] = 1;
times[1] = 19;
addresses[1] = "建设路2号";
states[1] = 1;
sumPrices[1] = 25.0;
/* 实现菜单切换 */
System.out.println("欢迎使用“吃货联盟订餐系统”");
int num = 1;// 用户输入0返回主菜单否则退出系统
boolean isExit = false;// 标记用户是否退出系统，true为退出
// 循环控制用户输入选择并执行
do {
System.out.println("************************");
System.out.println("1、我要订餐");
System.out.println("2、查看餐袋");
System.out.println("3、签收订单");
System.out.println("4、删除订单");
System.out.println("5、我要点赞");
System.out.println("6、退出系统");
System.out.println("************************");
System.out.print("请选择：");
num = input.nextInt();// 用户输入所要选择进行的操作
/* 使用switch结构来建立选择内容 */
switch (num) {
case 1:// 我要订餐
System.out.println("***我要订餐***");
boolean isAdd = false;// 记录是否可以点餐
for (int i = 0; i names.length; i++) {
if (names[i] == null) {
isAdd = false;
System.out.print("请输入订餐人姓名：");
String name = input.next();
System.out.println("序号" + "\t" + "菜名" + "\t\t" + "单价" + "\t" + "点赞数");
for (int j = 0; j dishNames.length; j++) {
System.out.println(
(j + 1) + "\t" + dishNames[j] + "\t\t" + prices[j] + "元" + "\t" + praiseNums[j]);
}
System.out.print("请选择您要点的菜品编号：");
int chooseDish = input.nextInt();
String dishMeg = dishNames[chooseDish - 1];
System.out.print("请选择您需要的份数：");
int number = input.nextInt();
System.out.print("请输入送餐时间（送餐时间是10点至20点间整点送餐）：");
int time = input.nextInt();
while (time 10 || time 20) {
System.out.print("您的输入有误，请输入10-20间的整数");
time = input.nextInt();
}
System.out.print("请输入送餐地址：");
String address = input.next();
// 默认可以预定，不用写订单状态
System.out.println("订餐成功！");
System.out.println("您定的是：" + dishNames[chooseDish - 1] + number + "份");
System.out.println("送餐时间：" + time + "点");
double sumPrice = prices[chooseDish - 1] * number;// 计算餐费
double sendMoney = (sumPrice = 50) ? 0 : 5;// 计算送餐费
System.out.println("餐费：" + sumPrice + "元，" + "送餐费" + sendMoney + "元，" + "总计："
+ (sumPrice + sendMoney) + "元。");
// 添加数据
names[i] = name;
dishMegs[i] = dishMeg;
times[i] = time;
dishNums[i] = number;
addresses[i] = address;
sumPrices[i] = sumPrice + sendMoney;
break;
}
if (isAdd) {
System.out.println("对不起，您的餐袋已满！");
}
}
break;
case 2:// 查看餐袋
System.out.println("***查看餐袋***");
System.out.println("序号\t订餐人\t餐品名称\t餐品数量\t送餐时间\t送餐地址\t总金额\t订单状态");
for (int i = 0; i names.length; i++) {
if (names[i] != null) {
String state = (states[i] == 0) ? "已预订" : "已完成";
System.out.println((i + 1) + "\t" + names[i] + "\t" + dishMegs[i] + "\t" + dishNums[i] + "份"
+ "\t" + times[i] + "\t" + addresses[i] + "\t" + sumPrices[i] + "元" + "\t" + state);
}
}
break;
case 3:// 签收订单
System.out.println("***签收订单***");
boolean isSignFind = false;
System.out.print("请选择要签收的订单序号：");
int sign = input.nextInt();
for (int i = 0; i names.length; i++) {
if (names[i] != null states[i] == 0 sign == i + 1) {
states[i] = 1;
System.out.println("订单签收成功！");
isSignFind = true;// 标记已找到的订单
} else if (names[i] != null states[i] == 1 sign == i + 1) {
System.out.println("您选择的订单已完成签收，不能再次签收！");
isSignFind = true;// 标记已找到的订单
}
}
if (!isSignFind) {
System.out.println("您选择的订单不存在！");
}
break;
case 4:// 删除订单
System.out.println("***删除订单***");
boolean isDelFind = false;
System.out.print("请输入要删除的订单序号：");
int delID = input.nextInt();
for (int i = 0; i names.length; i++) {
// 根据状态值判断能不能删除，只有已完成的才能删除
if (names[i] != null states[i] == 1 delID == i + 1) {
isDelFind = true;
for (int j = delID - 1; j names.length - 1; j++) {
names[j] = names[j + 1];
dishMegs[j] = dishMegs[j + 1];
dishNums[j] = dishNums[j + 1];
times[j] = times[j + 1];
addresses[j] = addresses[j + 1];
states[j] = states[j + 1];
sumPrices[j] = sumPrices[j + 1];
}
// 将最后一位清空
names[names.length - 1] = null;
dishMegs[names.length - 1] = null;
dishNums[names.length - 1] = 0;
times[names.length - 1] = 0;
addresses[names.length - 1] = null;
states[names.length - 1] = 0;
sumPrices[names.length - 1] = 0;
System.out.println("删除订单成功！");
break;
} else if (names[i] != null states[i] == 0 delID == i + 1) {
isDelFind = true;
System.out.println("您选择的订单未签收，不能删除！");
break;
}
} // 未找到的订单不能删除
if (!isDelFind) {
System.out.println("您要删除的订单不存在！");
}
break;
case 5:// 我要点赞
System.out.println("***我要点赞***");
// 显示菜品信息
System.out.println("序号\t菜名\t单价");
for (int i = 0; i dishNames.length; i++) {
String priaiseNum = (praiseNums[i] 0) ? praiseNums[i] + "赞" : "";
System.out.println((i + 1) + "\t" + dishNames[i] + "\t" + prices[i] + "元" + priaiseNum);
}
System.out.print("请选择您要点赞的菜品序号：");
int number = input.nextInt();
praiseNums[number - 1]++;
System.out.println("点赞成功");
break;
case 6:// 退出系统
isExit = true;
break;
default:// 退出系统
isExit = true;
break;
}
// 返回主界面
if (!isExit) {
System.out.print("输入0返回：");
num = input.nextInt();
} else {
break;
}
} while (num == 0);
System.out.println("谢谢惠顾，欢迎您再次使用！");
input.close();
}
}
首先 Student stu[]=new Student[100]; 只是定义了 一个引用的数组 stu数组里放的是指向null的空的引用 并不指向Student的实例 因为你没有new Student();运行时 会报空指针异常你应该 在前面new一个Studentstu[0] = new Student();
