Question

我需要检查用户是否输入数字（双精度）或字符串，除最后一部分外，一切都很完美。如果用户输入＆＃34; hello＆＃34;，程序将要求输入有效数字，但它无法正常工作。它给了我一个无限循环，除非我进入空间＆＃34; ＆＃34;

这是我的代码：

double bill = 0.0;
System.out.print("Please enter the total amount of your bill > ");
  String strAmount = keysIn.nextLine();
  try {
    bill = Double.parseDouble(strAmount);
    while (bill < 0) {
        System.out.print("Your bill amount is less then 0, try again > ");
        bill = keysIn.nextDouble();
      }
  } catch(NumberFormatException e) {
      while (!strAmount.isEmpty()) {
        System.out.print("Enter a valid number > ");
        strAmount = keysIn.nextLine();
      }
  }

感谢。

Answer 1

你有两个while循环检查不同的条件。试试这个：

double bill = 0.0;
System.out.print("Please enter the total amount of your bill > ");
String strAmount = keysIn.nextLine();
String numberString = strAmount.trim();

boolean invalidNumber = false;

 try {
   bill = Double.parseDouble(numberString);
 } catch(NumberFormatException e) {
   Systeout.print("Enter a valid number...");
   invalidNumber = true;
 }



while (bill < 0) {
    if(invalidNumber){
        System.out.print("Enter a valid number...");
    } else {
        System.out.println("Your bill amount is less then 0, try again...");
    }
    strAmount = keysIn.nextLine();
    numberString = strAmount.trim();

    try {
        bill = Double.parseDouble(numberString);
        invalidNumber = false;
    } catch(NumberFormatException e) {
        invalidNumber = true;
    }
  }

}

Answer 2

您的无限循环归因于while (!strAmount.isEmpty())，这意味着只要strAmount 不为空，它就会循环播放，因此删除!并移动检查循环结束。

        do {
            System.out.print("Enter a valid number > ");
            strAmount = keysIn.nextLine();
        } while (strAmount.isEmpty());

Answer 3

你可以试试这个：

double bill = 0.0;
    System.out.print("Please enter the total amount of your bill > ");
      String strAmount = keysIn.nextLine();
      boolean validated = false;

      //Validate
      while(!validated){
          try{
              bill = Double.parseDouble(strAmount);
              validated = true;
          }
          catch(NumberFormatException e) {
              System.out.print("Enter a valid number > ");
              strAmount = keysIn.nextLine();
          }
      }

      //Continue...
      while (bill < 0) {
        System.out.print("Your bill amount is less then 0, try again > ");
        bill = keysIn.nextDouble();
      }

Answer 4

一直尝试使用Scanner.nextDouble（）而不是一次。它只接受双打。

double bill = 0.0;
System.out.print("Please enter the total amount of your bill > ");
bill = keysIn.nextDouble();
while (bill < 0) {
    System.out.print("Your bill amount is less then 0, try again > ");
    bill = keysIn.nextDouble();
}

循环时的字符串

4 个答案: