try/catch with InputMismatchException creates infinite loop

Question

So I'm building a program which takes ints from user input. I have what seems to be a very straightforward try/catch block which, if the user doesn't enter an int, should repeat the block until they do. Here's the relevant part of the code:

import java.util.InputMismatchException; import java.util.Scanner;   public class Except {     public static void main(String[] args) {         Scanner input = new Scanner(System.in);         boolean bError = true;         int n1 = 0, n2 = 0, nQuotient = 0;          do {             try {                 System.out.println("Enter first num: ");                 n1 = input.nextInt();                 System.out.println("Enter second num: ");                 n2 = input.nextInt();                 nQuotient = n1/n2;                 bError = false;             }              catch (Exception e) {                 System.out.println("Error!");             }         } while (bError);          System.out.printf("%d/%d = %d",n1,n2, nQuotient);     } } 

If I enter a 0 for the second integer, then the try/catch does exactly what it's supposed to and makes me put it in again. But, if I have an InputMismatchException like by entering 5.5 for one of the numbers, it just shows my error message in an infinite loop. Why is this happening, and what can I do about it? (By the way, I have tried explicitly typing InputMismatchException as the argument to catch, but it didn't fix the problem.

Answer 1

You need to call next(); when you get the error. Also it is advisable to use hasNextInt()

       catch (Exception e) {             System.out.println("Error!");            input.next();// Move to next other wise exception         } 

Before reading integer value you need to make sure scanner has one. And you will not need exception handling like that.

    Scanner scanner = new Scanner(System.in);     int n1 = 0, n2 = 0;     boolean bError = true;     while (bError) {         if (scanner.hasNextInt())             n1 = scanner.nextInt();         else {             scanner.next();             continue;         }         if (scanner.hasNextInt())             n2 = scanner.nextInt();         else {             scanner.next();             continue;         }         bError = false;     }     System.out.println(n1);     System.out.println(n2); 

Javadoc of Scanner

When a scanner throws an InputMismatchException, the scanner will not pass the token that caused the exception, so that it may be retrieved or skipped via some other method.