Java 初学者需要建议吗？如果(金额==字符串)？

Question

我正在练习 java 银行帐户中的一些简单任务，需要有关代码块的建议，如何编写？这是一个例子，如果用户输入字符串或一些字母而不是数字来打印“请输入数字”，如何输入 Else if block amount == String，例如，很多 thx

            case 2:
            int amount = 0;
            System.out.println("Amount to withdraw:");
            amount = in.nextInt();
            if(amount <= 0)
            {
                System.err.println("you cannot withdraw negative amount!");
            }
            else if(amount > balans)
            {
                System.err.println("Not enough money on account!");
            }
            else if(...) // Here l need that
            {
                System.err.println("please enter a number instead of letters");
            }
            else
            {
                balans-=amount;
                System.out.println("You have successfully withdrawn " + amount + " €");
            }

Answer 1

在将其存储到amount 之前，只需检查用户提供的值的类型。您可以为此使用 in.hasNextInt。如果它不是Integer，请用户重新输入正确的值。

你可以尝试类似的东西

System.out.print("write Integer: ");
while(!in.hasNextInt()){      //used didn't provide valid value
    String value = in.next(); //lets consume it so Scanner can read and test next value
    System.out.println(value +" is not considered valid Integer.");
    System.our.print("please try again: ");
}
//here we are sure that user provided proper integer
amount = in.nextInt();

//and now we can proceed with rest of code
if(amount <= 0){
   ...
}

您还可以添加尝试计数器，如果用户尝试 3 次就退出程序，则不会提供正确的值。