Asking for input after catching an exception

Question

I want the user to enter a number which is scanned by the following code:

scanner.nextInt();

If a user enters a string instead, the program throws InputMismatchException, which is obvious. I want to catch the exception in such a way that the program prompts the user to enter an input until the user enters an integer value.

Scanner scanner = new Scanner(System.in);
while(true) {
    try {
        System.out.println("Please enter a number: ");
        int input = scanner.nextInt();
        System.out.println(input);
        //statements
        break;
    }
    catch(InputMismatchException | NumberFormatException ex ) {
        continue;
    }
}

This code creates an infinite loop if a string is entered.

You may need to reset the `Scanner` (I've no real experience with the class, but I've seen it done else where), try `scanner.reset()` before the `continue` — MadProgrammer, Aug 30 '12 at 06:48

score 4 · Answer 1 · answered Aug 31 '12 at 04:54

The answer to my problem is as follows:

Scanner scanner = new Scanner(System.in);
while(true) {
    try {
        System.out.println("Please enter a number: ");
        int input = scanner.nextInt();
        System.out.println(input);
        //statements
        break;
    }
    catch(InputMismatchException | NumberFormatException ex ) {
        scanner.next();//new piece of code which parses the wrong input and clears the //scanner for new input
        continue;
    }
}

sp00m · Accepted Answer · 2012-08-30T08:03:56.430

3

Put Scanner scanner = new Scanner(System.in); within your while loop.

Scanner scanner;
while(true) {    
    try {
        System.out.println("Please enter a number: ");
        scanner = new Scanner(System.in);
        int input = scanner.nextInt();
        System.out.println(input);
        //statements
        break;
    }
    catch(InputMismatchException | NumberFormatException ex ) {
        System.out.println("I said a number...");
    }
}

edited Aug 30 '12 at 08:03

answered Aug 30 '12 at 06:49

sp00m

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what you said works but I have defined the scanner object out side the method itself. In other words, it's a class variable. Is there a way to do so without creating the object within the try-catch statement? – h-rai Aug 30 '12 at 07:05
Of course, just reinstanciate the same object each loop. See the edit. – sp00m Aug 30 '12 at 08:04

score 0 · Answer 3 · answered Aug 30 '12 at 06:58

How about this?

while(true) {    
    try {
        System.out.println("Please enter a number: ");
        Scanner scanner = new Scanner(System.in);
        int input = scanner.nextInt();
        System.out.println("\n\nEntered number is : " + input);
        break;
    } catch(InputMismatchException | NumberFormatException ex ) {
        System.out.println("\n\nInput was not a number. Please enter number again : ");
    } catch(Exception e ) {
        System.out.println("\n\nException caught :: " + e);
    }
}

I have also removed continue syntax as those are not needed.

Asking for input after catching an exception

3 Answers3