Java ATM 程序

Question

我正在做一个自动取款机程序，我很难弄清楚如何让它实际存款和取款。余额一开始自动为 0 美元，但我无法输入任何内容来实际添加或减去它，我做错了什么？

public class ATM {
static Scanner keyboard = new Scanner(System.in);
static String acctNum, pwd, result;
static double oldBalance, newBalance, deposit, withdraw;
static int choose;

public static void main(String[] args) {
    for (int run = 0; run < 3; run++) {
        System.out.println("Enter your account number");
        acctNum = keyboard.nextLine();
        System.out.println("Enter your account password");
        pwd = keyboard.nextLine();

        result = checkID(acctNum, pwd);
        if (!result.equals("ERROR")) {
            break;
        } else if (run == 2) {// you cannot try to log in anymore than 3
                                // times
            System.out.println("MAXIMUM TRIES EXCEEDED");
            return;
        }

    }
    menu();
}

public static String checkID(String acctNum, Object pwd) {
    String result = "ERROR";
    String a = "44567-5 mypassword 520.36";
    String b = "1234567-6 anotherpassword 48.20";
    String c = "4321-0 betterpassword 96.74";

    if (acctNum.equals("44567-5") && pwd.equals("mypassword")) {
        result = "520.36";
    } else if (acctNum.equals("1234567-6") && pwd.equals("anotherpassword")) {
        result = "48.20";
    } else if (acctNum.equals("4321-0") && pwd.equals("betterpassword")) {
        result = "96.74";
    }
    System.out.println(result);
    return result;
}

public static int menu() {
    System.out
            .println("Choose one of the following: \n1.Display Balance\n2.Deposit\n3.Withdraw\n4.Log Out");
    choose = keyboard.nextInt();

    if (choose == 1) {// 1. Display Balance
        displayBalance();
        menu();
        return 1;

    }
    if (choose == 2) {// 2. Deposit
        deposit();
        menu();
        return 2;

    }
    if (choose == 3) {// 3. Withdraw
        withdraw();
        menu();
        return 3;

    }
    if (choose == 4) {// 4. Log out
        System.out.println("You are logged out.");
        return 4;

    }
    if (choose <= 5) {// type in anything greater than 4 and you will get a
                        // system error
        System.out.println("System Error");
        menu();
        return 5;
    }
    if (choose >= 1) {// type in anything less than 1 and you will get a
                        // system error
        System.out.println("System Error");
        menu();
        return 6;
    }
    return choose;

}

public static double deposit() {
    System.out.println("How much would you like to deposit?");
    deposit = keyboard.nextInt();
    System.out.println((deposit + oldBalance)==newBalance);// deposit money into balance
    return 2;
}

public static double displayBalance() {
    System.out.println("Total balance is: $" + oldBalance);
    oldBalance = 0.00;
    return 1;
}

public static double withdraw() {
    System.out.println("How much would you like to withdraw?");
    withdraw = keyboard.nextInt();
    System.out.println(newBalance + withdraw);// withdraw money from balance
    return 3;
}

}

Answer 1

一些观察:

1. 您的类不应将 oldBalance、存款和取款声明为全局变量。提款方法不应访问存款变量，反之亦然。尽可能限制变量的范围是一种很好的编程习惯。因为此方法之外实际上并不需要“deposit”变量，所以绝对没有理由将其设为全局变量。对于“当前余额”则不能这样说。类的所有方法都需要此变量:存款、取款、displayBalance 等。因此，有充分的理由将其设为全局(不过，如果您可以用较小的范围解决问题，您应该这样做)。

2. 我不明白为什么 deposit() 和 withdrawal() 需要返回任何内容。

deposit() 和 withdrawal() 最简单的实现是将用户输入添加到 currentBalance 并将其保存在当前余额。

public void deposit()
{
   Scanner input = new Scanner(System.in);
   System.out.printn("Enter deposit amount: );
   double amount = input.nextDouble();
   System.out.println("Your deposit amount: " + amount);
   currentBalance += amount;
   System.out.println("Your new balance is: + currentBalance);
}

public void withdrawal()
{
   Scanner input = new Scanner(System.in);
   System.out.printn("Enter withdrawal amount: );
   double amount = input.nextDouble();
   System.out.println("Your withdrawal amount: " + amount);
   currentBalance -= amount;
   System.out.println("Your new balance is: + currentBalance);
}

您永远不会保存当前余额。 == 运算符是比较运算符，而不是赋值运算符。当你做这样的事情时:

System.out.println((deposit + oldBalance)==newBalance);

或者像这样:

System.out.println(newBalance + withdraw);

您所做的只是将值传递给 println() 方法，而不是更新应该保持平衡的变量。事实上，第一个应该打印 false (除非 Deposit 和 oldBalance 都为零)。如果您查看我的代码示例，currentBalance += amount; 是 currentBalance = currentBalance + amount; 的简写，意思是“将此 amount 添加到currentBalance 并将其存储在 currentBalance 中。因为我重用了 currentBalance，所以不再需要 oldBalance 变量。