Question

我有以下代码会导致无限循环：

System.out.println("Adjust Invoices");
System.out.println("Would like to Pay an invoice or Add an invoice to your account?");
System.out.println("Press '1' to Pay and '2' to Add");
int invoice = choice.nextInt();
do
{
    if (invoice == 1)
    {
        System.out.println("one");
    }
    if (invoice == 2)
    {
        System.out.println("two");
    }
    else
    {
        System.out.println("Press '1' to Pay and '2' to Add");
    }
} while (invoice >= 3 || invoice <=0);

当我输入“ 1”或“ 2”以外的内容时，如何阻止它成为无限循环？

Answer 1

好吧，我想首先您必须放上

int invoice = choice.nextInt();

在循环内部避免这种情况。否则，使用循环是没有意义的。如果输入错误，您想循环播放，对吗？好吧，这只有在您允许用户纠正他们的输入的情况下才有意义。

然后，只要出现有效输入，我就冒汗，并在没有“ else”的情况下将提示打印在最后。另外，如果您在这些时间点中断，则可以删除条件。这将是多余的。您的提示也是多余的，因此只需在输入之前输入提示。因此，您最终得到的是：

System.out.println("Adjust Invoices");
    System.out.println("Would like to Pay an invoice or Add an invoice to your account?");

    int invoice;
    do
    {
        System.out.println("Press '1' to Pay and '2' to Add");
        invoice = choice.nextInt();
        if (invoice == 1)
        {
            System.out.println("one");
            break;
        }
        if (invoice == 2)
        {
            System.out.println("two");
            break;
        }
    } while (true);

Answer 2

要阻止循环无限循环，必须避免该条件保持为真，否则它不会停止。如果要在根据情况做出响应后停止循环，请中断循环。

对于您的情况，您可以按照以下步骤进行操作（请记住，如果第一个值未经验证，则必须选择另一个值，这就是为什么invoice=choice.nextInt()必须包含在循环的顶部）：

do
     {
          invoice = choice.nextInt();
          if(invoice == 1)
          {
                 System.out.println("one");
                 break;
                 //quit the loop after the operation
          }
          else if (invoice == 2)
          {//we add else if because invoice might be either 1 or 2 or another value and not two values at same time.
                System.out.println("two");
                //quit the loop after the operation
          }
         else
         {
                   System.out.println("Press '1' to Pay and '2' to Add");
                   //don't break here because you are just leaving a message to let the user know invoice must be either one or two and if not display the message
          }
    }while(invoice >= 3 || invoice <=0);

Answer 3

确定输入<1>或'2'以外的内容时是否要停止循环？
通常的做法是，当用户输入有效选择1或2时，停止这种循环，并给出诸如0之类的另一种退出选项。
因此，只要用户未输入1或2，循环就不会结束：

Scanner choice = new Scanner(System.in);
System.out.println("Adjust Invoices");
System.out.println("Would like to Pay an invoice or Add an invoice to your account?");

int invoice;

do {
    System.out.println("Press '1' to Pay or '2' to Add, '0' to Exit");
    invoice = choice.nextInt();
    if (invoice == 0) {
        System.out.println("Exiting...");
        break;
    } else if(invoice == 1) {
        System.out.println("one");
        break;
    } else if (invoice == 2) {
        System.out.println("two");
        break;
    } 
} while(invoice < 0 || invoice > 2);

我如何停止do ... while循环成为无限循环

3 个答案: