Question

在下面的SSCCE中，为什么catch块一次又一次地执行，导致无限循环？

当我运行此程序并提示输入整数时，我输入a。

我认为会发生的是InputMismatchException会在try块内的第一行抛出，然后控件将转到catch块，它将打印``一次，然后进入while(true)循环的下一次迭代，它应该再次进入try块并且应该提示我输入整数。

但是一旦它进入while(true)循环，似乎已经开始无休止地进入catch块，因为如果它进入try块，它会促使我再次输入一个整数。 / p>

哪里，哪个是错误？

import java.util.InputMismatchException;
import java.util.Scanner;


public class WhyThisInfiniteLoop {

    public static void main (String [] args) {
        Scanner reader = new Scanner(System.in); 
        int i = 0; 
        System.out.println("Please enter an integer: ");

        while(true){
          try{
             i = reader.nextInt();
             break;  
          }catch(InputMismatchException ex){
             System.out.println("You did not enter an int. Please enter an integer:");
          }
        }

        System.out.println("Input of type int: " + i);
    }

}

输出

Please enter an integer:
a
You did not enter an int. Please enter an integer:
You did not enter an int. Please enter an integer:
You did not enter an int. Please enter an integer:
You did not enter an int. Please enter an integer:
You did not enter an int. Please enter an integer:
You did not enter an int. Please enter an integer:
You did not enter an int. Please enter an integer:
You did not enter an int. Please enter an integer:
You did not enter an int. Please enter an integer:
You did not enter an int. Please enter an integer:
You did not enter an int. Please enter an integer:
You did not enter an int. Please enter an integer:
You did not enter an int. Please enter an integer:
You did not enter an int. Please enter an integer:
You did not enter an int. Please enter an integer:
You did not enter an int. Please enter an integer:
You did not enter an int. Please enter an integer:
You did not enter an int. Please enter an integer:
You did not enter an int. Please enter an integer:
You did not enter an int. Please enter an integer:
You did not enter an int. Please enter an integer:
You did not ...
...
...

Answer 1

因为您没有在int块中读取不是catch的内容（令牌）。尝试像

这样的东西

try {
    i = reader.nextInt();
    break;  
} catch (InputMismatchException ex) {
    System.out.printf("%s is not an int. Please enter an integer:", reader.next());
}

调用reader.next()（将使用令牌）就足够了。

按原样，您的Scanner说nextInt会导致错误，即没有int。然后循环尝试读取int（以及失败）。

为什么控件直接进入catch块而不进入此SSCCE中的try块？

1 个答案: