Java Scanner/Input Help(输入不匹配异常)

Question

atm 程序。当您按数字时，它会将您重定向到一个选项。前任。 2 = 存款。它要求提取金额或按“b”进入主菜单。如果您输入存款金额，则可以正常工作。如果按“b”进入主菜单，它将不起作用并发送输入不匹配异常

static double balance = 0.0;
public static void deposit(double amount)
{
    balance = balance + amount;
}

public static void withdraw(double amount)
{
    balance = balance - amount;
}


private static void transaction()
{
    Scanner input = new Scanner(System.in);
    System.out.println("Welcome to the ATM");
    System.out.println("1 for balance\n2 for deposit\n3 for withdraw");
    int choice = input.nextInt();
    switch (choice) {
    case 1:
        System.out.println("Your balance is " + balance);

        transaction();
    case 2:
        System.out.println("Enter the amount or 'b' to go back");
        if (input.nextLine() == "b")
        {
        transaction();
        }
        else 
        {
        deposit(input.nextDouble());
        System.out.println("Success!");
        transaction();
        }***
    case 3:
        if (balance >= 0)
        {
            System.out.println("Your balance is negative!");
        }
        else
        {
        System.out.println("Enter the amount");
        withdraw(input.nextDouble());
        System.out.println("Success!");
        transaction();
        }
    default:
        System.out.println("Enter a valid option");
        transaction();
    }
}

Answer 1

使用 .quals() 而不是 == 进行相等性检查 -

input.nextLine().equals("b")

奖金建议:

您不应直接在 if() 内获取输入，而应首先将用户输入作为 String 获取。然后检查它的 b 是否，否则将其转换为 double 并存入!

String userInput = input.next();

if (userInput.equals("b")) {
    transaction();
} else {
    try {
        double depositAmount = Double.parseDouble(userInput);
        deposit(depositAmount);
    } catch (NumberFormatException ex) {
        System.out.println("Invalid input");
    }
}