使用If语句中的临时值继续尝试捕获

2 回答

• -1

  您只需将变量的初始化放在try和catch块中，如下所示：

  try {
      double tempValue = scan.nextDouble();
  } catch (InputMismatchException ex) {
      System.out.println("Please enter a number.");
  }
  

  回复于 2024-05-01T08:11:13+08:00
• 1

  在catch语句中，您使用 scan.nextLine() ，但是您应该使用 scan.nextDouble() ，就像在主循环中一样 . 也就是说，你想接受双打作为输入 . 此外，您的try / catch语法似乎是错误的 . 您希望捕获可能由用户输入引起的错误;因此，您需要添加用户在 try 块中输入内容的代码 . 见下文：

  try {
              double tempValue = scan.nextDouble();
  
              //this loop will keep spinning, until tempValue is valid
              while (tempValue > 100d || tempValue < 0d) {
                  System.out.println("Invalid. Try again. Range is 0 - 100");
                  tempValue = scan.nextDouble();
              }
              //this loop will spin forever (There is nothing to terminate it)
              while (true) {
  
                  double sumFocus = 0;
                  double[] arrayFocus = new double[2];
  
                  for (int i = 0; i < 2; i++) {
                      arrayFocus[i] = scan.nextDouble();
                  }
                  for (double num : arrayFocus) {
                      sumFocus = sumFocus + num;
                  }
              }
          }
          catch (InputMismatchException e) {
  
              System.out.println("Invalid input");
              scan.nextDouble(); //this doesn't do anything. The value is not assigned to any variable
          }
  

  使用上面的代码，当用户输入无效字符时，例如：字母，然后程序将停止 . 为什么？因为catch在无限循环之外，这使得程序计数器移出循环，当执行catch语句中的代码时，程序也会在到达结束时终止 .

  你能做什么，是这样的：

  static double validValueWithRange(Double min, Double max){
     Scanner s = new Scanner(System.in);
     System.out.println("Enter a valid value for a 'double': ");
     double value;
     try {
         value = s.nextDouble();
         if(value > max || value < min){
           System.out.println("Invalid. Try again. Range is 0 - 100");
           return validValueWithRange(min, max);
         }
      }
      catch (InputMismatchException e) {
          System.out.println("Invalid input. Try again.");
          return validValueWithRange(min, max);
      }
  
      return value;
  }
  
  static double validValue(){
      Scanner s = new Scanner(System.in);
      System.out.println("Enter a valid value for a 'double': ");
      double value;
      try {
          value = s.nextDouble();
      }
      catch (InputMismatchException e) {
          System.out.println("Invalid input. Try again.");
          return validValue();
      }
  
      return value;
  }
  
  public static void main(String[] args){
      Scanner scan = new Scanner(System.in);
  
      double tempValue = validValueWithRange(0d, 100d);
  
      while (true) {
          System.out.println("Now entering endless while loop");
          double sumFocus = 0;
          double[] arrayFocus = new double[2];
  
          for (int i = 0; i < 2; i++) {
              arrayFocus[i] = validValue();
          }
          for (double num : arrayFocus) {
              sumFocus = sumFocus + num;
          }
      }
  }
  

  回复于 2024-05-01T08:11:13+08:00