方法与数组综合项目：控制台系统的同框架迁移实训

import java.util.Scanner;

public class SupermarketSystem {
    static Scanner sc = new Scanner(System.in);

    public static void main(String[] args) {
        String[] names = new String[100];   // 商品名池
        float[] prices = new float[100];    // 价格池，与 names 下标一一对应
        int count = 0;                      // 当前商品数

        while (true) {                      // 死循环 = 常驻服务
            int choice = Menu(names, prices, count);
            if (choice == 4) {              // 退出选项
                Back();
                break;                      // 唯一的出口
            }
            count = dispatch(choice, names, prices, count);
        }
    }

    static int Menu(String[] names, float[] prices, int count) {
        System.out.println("==== 超市管理系统 ====");
        System.out.println("1. 添加商品");
        System.out.println("2. 显示全部商品");
        System.out.println("3. 查询最贵与最便宜");
        System.out.println("4. 退出");
        System.out.print("请选择：");
        int choice = sc.nextInt();
        return choice;
    }

    static int dispatch(int choice, String[] names, float[] prices, int count) {
        switch (choice) {
            case 1:  return AddGoods(names, prices, count);
            case 2:  ShowGoods(names, prices, count);  return count;
            case 3:  FindMaxAndMinGoods(names, prices, count); return count;
            default:
                System.out.println("无此选项，请重新输入");
                return count;
        }
    }
}

static int AddGoods(String[] names, float[] prices, int count) {
    if (count >= names.length) {            // 先判满，再存
        System.out.println("仓库已满");
        return count;
    }
    System.out.print("商品名：");
    names[count] = sc.next();
    System.out.print("价格：");
    prices[count] = sc.nextFloat();
    System.out.println("已添加：" + names[count]);
    return count + 1;                        // 数量 +1 由返回值带出
}

static void ShowGoods(String[] names, float[] prices, int count) {
    if (count == 0) {
        System.out.println("暂无商品");
        return;                              // 空数据提前返回，防for白跑
    }
    for (int i = 0; i < count; i++) {        // 只遍历到 count，不遍历整个数组
        System.out.printf("%d. %s  %.2f 元%n", i + 1, names[i], prices[i]);
    }
}

static void FindMaxAndMinGoods(String[] names, float[] prices, int count) {
    if (count == 0) { System.out.println("暂无商品"); return; }

    int maxIdx = 0, minIdx = 0;              // 记下标而不是记价格值
    for (int i = 1; i < count; i++) {
        if (prices[i] > prices[maxIdx]) maxIdx = i;
        if (prices[i] < prices[minIdx]) minIdx = i;
    }
    System.out.printf("最贵：%s %.2f 元%n", names[maxIdx], prices[maxIdx]);
    System.out.printf("最便宜：%s %.2f 元%n", names[minIdx], prices[minIdx]);
}

static void Back() {
    System.out.println("感谢使用，再见");
}

static void SettleTeas(String[] names, float[] prices, int count) {
    float total = 0;                          // 本单合计
    while (true) {
        ShowGoods(names, prices, count);      // 每轮重显菜单，让顾客看着选
        System.out.print("请输入饮品编号（0 结束购买）：");
        int no = sc.nextInt();
        if (no == 0) break;                   // 0 号 = 结账离场
        if (no < 1 || no > count) {           // 编号合法性先校验
            System.out.println("编号错误，请重新输入");
            continue;                          // 跳回循环开头，不累计
        }
        float price = prices[no - 1];         // 编号转下标：差 1
        total += price;
        System.out.printf("已选 %s，当前合计 %.2f 元%n", names[no - 1], total);
    }
    System.out.printf("本单合计：%.2f 元%n", total);
}

public class BankMange1 {
    static double balance = 5000;   // 初始余额随机产生亦可：(int)(Math.random()*10000)

    public static void main(String[] args) {
        if (Login()) {
            Menu();
        }
    }

    static boolean Login() { /* 三次机会，成功 true */ ... }

    static void Menu() {
        while (true) {
            System.out.println("1.查询 2.取款 3.转账 4.退卡");
            int choice = new Scanner(System.in).nextInt();
            switch (choice) {
                case 2:
                    balance = BankDraw(balance);   // 余额经返回值回传
                    break;
                case 4: return;                     // 退卡即结束
                default: System.out.println("无此功能");
            }
        }
    }

    static double BankDraw(double current) {
        System.out.print("取款金额：");
        double amount = new Scanner(System.in).nextDouble();
        if (amount > current) {
            System.out.println("余额不足");
            return current;                          // 失败也返回原值
        }
        return current - amount;                     // 成功返回新值
    }
}

static double balance;   // 全局变量

static void BankDraw() {
    balance = balance - amount;   // 方法内部直接改，无参数无返回值
}

static boolean Login() {
    Scanner sc = new Scanner(System.in);
    int i = 1;                                  // 已尝试次数
    while (i <= 3) {
        System.out.print("账号：");
        String id = sc.next();
        System.out.print("密码：");
        String pwd = sc.next();
        if (id.equals("1234") && pwd.equals("5678")) {
            System.out.println("登录成功");
            return true;
        } else {
            System.out.println("账号或密码错误，剩余 " + (3 - i) + " 次机会");
            i++;                                 // 关键：失败也要计数
        }
    }
    System.out.println("三次错误，账号已冻结");
    return false;
}

} else {
    if (i == 2) {
        System.out.println("请检查大小写锁定");
    } else if (i == 3 - 1 + 1) {   // 即 i == 3：最后一次机会前
        System.out.println("这是最后一次机会");
    }
    System.out.println("账号或密码错误，剩余 " + (3 - i) + " 次机会");
    i++;
}