程式碼：

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

public class CheckStand {

    static java.util.Scanner scanner = new java.util.Scanner(System.in);

    static Order custom1 = new Order();

    static int count = 0;
    static int counta = 0;
    static int isError = 0;
    static int orderNumber = 1;
    static double sum = 0.00;
    static int goodsNum = 0;
    static int amount = 0;
    static int minusAmount = 0;
    static int putawayNum = 0;
    static double putawayPrice = 0;
    static String putawayName = null;

    static String next, next2, next3;

    public static void main(String[] args) {
        while (true) {
            next = first();
            //使用
            if (next.equalsIgnoreCase("U")) {
                sum = 0.00;
                counta = 0;
                custom1.detailsInit(Order.goodsCenter);
                firstUse();
                orderNumber++;
                continue;
                //設定
            } else if (next.equalsIgnoreCase("S")) {
                firstSetUp();
                continue;
            } else if (next.equalsIgnoreCase("Q")) {
                custom1.quitMenu();
                System.exit(-1);
            }
        }
    }

    public static void firstUse() {
        while (true) {
            isError = 0;
            next2 = use();
            if (next2.equalsIgnoreCase("A")) {
                add();
                counta = 1;
                continue;
            } else if (next2.equalsIgnoreCase("S")) {
                custom1.details(orderNumber, sum, Order.goodsCenter);
                continue;
            } else if (next2.equalsIgnoreCase("D")) {
                reduce();
                continue;
            } else if (next2.equalsIgnoreCase("L")) {
                custom1.commodityList(Order.goods);
                continue;
            }
            if (next2.equalsIgnoreCase("Q")) {
                break;
            }
        }
    }

    public static void firstSetUp() {
        while (true) {
            isError = 0;
            next3 = setUp();
            if (next3.equalsIgnoreCase("A")) {
                putaway();
                count = 1;
                continue;
            } else if (next3.equalsIgnoreCase("S")) {
                continue;
            } else if (next3.equalsIgnoreCase("D")) {
                soldOut();
                continue;
            } else if (next3.equalsIgnoreCase("U")) {
                alter();
                continue;
            } else if (next3.equalsIgnoreCase("Q")) {
                break;
            }
        }
    }

    //第一層選單
    public static String first() {
        custom1.enterMenu();
        String letter;
        while (true) {
            letter = scanner.nextLine().trim();
            if (letter.equalsIgnoreCase("U")) {
                custom1.payMenu();
                if (count == 0) {
                    custom1.commodityListInit(Order.goods);
                }
                custom1.commodityList(Order.goods);
                break;
            } else if (letter.equalsIgnoreCase("S")) {
                custom1.setUpMenu();
                break;
            } else if (letter.equalsIgnoreCase("A")) {
                custom1.aboutMenu();
                continue;
            } else if (letter.equalsIgnoreCase("Q")) {
                break;
            } else {
                System.out.println("您的輸入有誤，請重新輸入：");
            }
        }
        return letter;
    }

    //進入使用介面
    public static String use() {
        String letter1;
        while (true) {
            isError = 0;
            letter1 = scanner.nextLine().trim();
            if (letter1.equalsIgnoreCase("S")) {
                break;
            } else if (letter1.equalsIgnoreCase("A")) {
                System.out.println("請輸入下單資訊[編號 數量]（如下格式：1 2）");
                break;
            } else if (letter1.equalsIgnoreCase("D")) {
                System.out.println("請輸入取消資訊[編號 數量]（如下格式：1 2）");
                break;
            } else if (letter1.equalsIgnoreCase("L")) {
                break;
            } else if (letter1.equalsIgnoreCase("Q")) {
                break;
            } else {
                System.out.println("您的輸入有誤，請重新輸入：");
                continue;
            }
        }
        return letter1;
    }

    //進入設定介面
    public static String setUp() {
        String letter;
        while (true) {
            letter = scanner.nextLine().trim();
            //檢視
            if (count == 0) {
                custom1.commodityListInit(Order.goods);
            }
            if (letter.equalsIgnoreCase("S")) {
                custom1.commodityList(Order.goods);
                break;
                //上架
            } else if (letter.equalsIgnoreCase("A")) {
                System.out.println("請輸入上架商品資訊（如下格式：1 餐巾紙 1.4）");
                break;
                //下架
            } else if (letter.equalsIgnoreCase("D")) {
                System.out.println("請輸入下架商品資訊（如下格式：1 ）");
                break;
                //修改
            } else if (letter.equalsIgnoreCase("U")) {
                System.out.println("請輸入修改商品資訊（如下格式：1 餐巾紙 1.4）");
                break;
            }
            //退出
            else if (letter.equalsIgnoreCase("Q")) {
                break;
            } else {
                System.out.println("您的輸入有誤，請重新輸入：");
                continue;
            }
        }
        return letter;
    }

    //上架
    public static void putaway() {
        if (count == 0) {
            custom1.commodityListInit(Order.goods);
        }
        while (true) {
            input();
            //若編號大於10，提示錯誤
            if (putawayNum > 10) {
                System.out.println("編號已超出範圍！請重新上架！");
                continue;
            }
            if (Order.goods[putawayNum - 1].name.equals("--[未上架]") == false) {
                System.out.println("您挑選的商品已上架，請重新上架！");
                continue;
            }
            break;
        }
        if(isError==0) {
            Order.goods[putawayNum - 1] = new Goods(putawayNum, putawayName, putawayPrice);
            custom1.commodityList(Order.goods);
        }
    }

    //下架
    public static void soldOut() {
        int putawayNum = 0;
        while (true) {
            String letter = scanner.nextLine().trim();
            //將使用者輸入賦給putawayNum
            try {
                putawayNum = Integer.parseInt(letter);
            } catch (NumberFormatException e) {
                e.printStackTrace();
            }
            //若編號大於10，提示錯誤
            if (putawayNum > 10) {
                System.out.println("編號已超出範圍！請重新下架！");
                continue;
            }
            if (Order.goods[putawayNum - 1].name.equals("--[未上架]")) {
                System.out.println("您挑選的商品還未上架，暫不能下架！");
                continue;
            }
            break;
        }
        Order.goods[putawayNum - 1] = new Goods(putawayNum, "--[未上架]", 0.0);
        custom1.commodityList(Order.goods);
    }

    // 修改
    public static void alter() {
        while (true) {
            input();
            //若編號大於10，提示錯誤
            if (putawayNum > 10) {
                System.out.println("編號已超出範圍！請重新上架！");
                continue;
            }
            if (Order.goods[putawayNum - 1].name.equals("--[未上架]")) {
                System.out.println("您挑選的商品還未上架，暫不能修改！");
                continue;
            }
            break;
        }
        if(isError==0){
            Order.goods[putawayNum - 1] = new Goods(putawayNum, putawayName, putawayPrice);
            custom1.commodityList(Order.goods);
        }
    }

    // 下單
    public static void add() {
        while (true) {
            input1();
            //若編號大於10，提示錯誤
            if (goodsNum > 10) {
                System.out.println("編號已超出範圍！請重新下單！");
                continue;
            }
            if (Order.goods[goodsNum - 1].name.equals("--[未上架]")) {
                System.out.println("您挑選的商品還未上架，請重新挑選！");
                continue;
            }
            break;
        }
        if (isError == 0) {
            String name = Order.goods[goodsNum - 1].name;
            double price = Order.goods[goodsNum - 1].price;
            if (Order.goodsCenter[goodsNum - 1].amount != 0) {
                amount += Order.goodsCenter[goodsNum - 1].amount;
                sum = price * amount;
            } else {
                sum += price * amount;
            }
            Order.goodsCenter[goodsNum - 1] = new GoodsCenter(goodsNum, name, amount, price);
            custom1.details(orderNumber, sum, Order.goodsCenter);
        }

    }

    // 取消
    public static void reduce() {
        while (true) {
            input1();
            minusAmount=amount;
            //若編號大於10，提示錯誤
            if (goodsNum > 10) {
                System.out.println("編號已超出範圍！請重新取消！");
                continue;
            }
            if (Order.goodsCenter[goodsNum - 1].amount == 0) {
                System.out.println("您還未挑選過此商品，請重新取消！");
                continue;
            }

            if (Order.goodsCenter[goodsNum - 1].amount < minusAmount) {
                System.out.println("該商品的取消數量超出已下單數量，請重新取消！");
                continue;
            }
            if (minusAmount < 0) {
                System.out.println("您的輸入有誤，請重新取消！");
                continue;
            }
            break;
        }

        if (isError == 0) {
            String name = Order.goods[goodsNum - 1].name;
            double price = Order.goods[goodsNum - 1].price;
            Order.goodsCenter[goodsNum - 1].amount -= minusAmount;
            Order.goodsCenter[goodsNum - 1] = new GoodsCenter(goodsNum, name, Order.goodsCenter[goodsNum - 1].amount, price);
            sum = sum + Order.goodsCenter[goodsNum - 1].price * amount - (amount + minusAmount) * Order.goodsCenter[goodsNum - 1].price;
            custom1.details(orderNumber, sum, Order.goodsCenter);
        }
    }

    public static void input() {
        String[] str;
        String letter = scanner.nextLine().trim();
        //將字串拆開
        str = letter.split(" ", 3);
        //將使用者輸入的第一部分賦給putawayNum
        try {
            putawayNum = Integer.parseInt(str[0].trim());
            //將使用者輸入的第二部分賦給putawayName
            putawayName = str[1].trim();
            //將使用者輸入的第三部分賦給putawayPrice
            putawayPrice = Double.valueOf(str[2].trim());
        } catch (NumberFormatException e) {
            System.out.println("您沒有按要求輸入！");
            isError = 1;
        }catch(ArrayIndexOutOfBoundsException e){
            System.out.println("您沒有按要求輸入！");
            isError = 1;
        }
    }

    public static void input1(){
        String[] str;
        String letter = scanner.nextLine();
        try {
            //將字串拆開
            str = letter.trim().split("", 2);
            //將使用者輸入的第一部分賦給orderNum
            goodsNum = Integer.parseInt(str[0].trim());
            //將使用者輸入的第二部分賦給amount
            amount = Integer.parseInt(str[1].trim());
        } catch (NumberFormatException e) {
            System.out.println("您沒有按要求輸入！");
            isError = 1;
        } catch (ArrayIndexOutOfBoundsException e) {
            System.out.println("您沒有按要求輸入！");
            isError = 1;
        }
    }
}

class Order {
    static Goods[] goods = new Goods[10];
    static GoodsCenter[] goodsCenter = new GoodsCenter[10];

    public void enterMenu() {
        System.out.println("***************歡迎使用簡易收銀臺***************");
        System.out.println("       [U]使用  [S]設定  [A]關於  [Q]退出       ");
        System.out.println("            輸入：U S A Q  進入操作             ");
        System.out.println("************************************************");
    }

    public void quitMenu() {
        System.out.println("************************************************");
        System.out.println("                歡迎使用，下次再見              ");
        System.out.println("************************************************");
    }

    public void aboutMenu() {
        System.out.println("**********************關於**********************");
        System.out.println("        名稱：簡易收銀臺                        ");
        System.out.println("        功能：基於字元介面的收銀臺作業系統      ");
        System.out.println("        作者：qqycc                             ");
        System.out.println("        版本：v0.0.1                            ");
        System.out.println("        意見反饋：*********@qq.com              ");
        System.out.println("************************************************");
    }

    public void setUpMenu() {
        System.out.println("********************設定功能********************");
        System.out.println("   [S]檢視  [A]上架  [D]下架  [U]修改  [Q]退出  ");
        System.out.println("            輸入：S A D U Q  進入操作           ");
        System.out.println("************************************************");
    }

    public void payMenu() {
        System.out.println("********************買單功能********************");
        System.out.println("   [S]檢視  [A]下單  [D]取消  [L]瀏覽  [Q]退出  ");
        System.out.println("            輸入：S A D L Q  進入操作           ");
        System.out.println("************************************************");
    }

    public void commodityListInit(Goods[] goods) {
        for (int i = 0; i < goods.length; i++) {
            goods[i] = new Goods(i + 1, "--[未上架]", 0.0);
        }
    }

    public void commodityList(Goods[] goods) {
        System.out.println("******************* 商品清單 *******************");
        System.out.println("\t   " + "編號" + "\t        " + "產品名稱" + "\t         " + "單價");
        for (int i = 0; i < goods.length; i++) {
            goods[i].printList();
        }
        System.out.println("************************************************");
    }

    public void detailsInit(GoodsCenter[] goodsCenter) {
        for (int i = 0; i < goodsCenter.length; i++) {
            goodsCenter[i] = new GoodsCenter(0, "", 0, 0.0);
        }
    }

    public void details(int orderNumber, double sum, GoodsCenter[] goodsCenter) {
        System.out.println("=======================================");
        System.out.println("編號：" + orderNumber);
        SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");//設定日期格式
        System.out.println("列印時間：" + df.format(new Date()));// new Date()為獲取當前系統時間
        System.out.println("=======================================");
        System.out.println("編號\t名稱\t數量\t單價");
        for (int i = 0; i < goodsCenter.length; i++) {
            if (goodsCenter[i].serialNumber == 0) {
                continue;
            }
            goodsCenter[i].printList();
        }
        System.out.println("=======================================");
        System.out.println("總價：" + String.format("%.2f", sum));
        System.out.println("=======================================");
    }
}

class GoodsCenter extends Goods {
    int amount;

    public GoodsCenter(int serialNumber, String name, int amount, double price) {
        super(serialNumber, name, price);
        this.amount = amount;
    }

    public void printList() {
        System.out.println(this.serialNumber + "\t" + this.name + "\t" + this.amount + "\t" + this.price);
    }
}

class Goods {
    int serialNumber;
    String name;
    double price;

    public Goods(int serialNumber, String name, double price) {
        this.serialNumber = serialNumber;
        this.name = name;
        this.price = price;
    }

    public void printList() {
        System.out.println("\t   " + this.serialNumber + "\t        " + this.name + "\t             " + this.price);
    }
}