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Thread: How to validate user input in a loop

  1. #1
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    Default How to validate user input in a loop

    Is there a method that allows me to check if the user entered anything other than an integer. For example I want the user only to enter an integer, I have this code.

     
    			try 
    			{
    		         integerVariable = sc.nextInt();
     
    			} 
    			catch(InputMismatchException e)
    			{
    		     System.err.println("try again, wrong type");
    			}
    		}

    That is only good for one time. How would I go about doing this in a loop say 5 times or something?


  2. #2
    Crazy Cat Lady KevinWorkman's Avatar
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    Default Re: How to validate user input in a loop

    Have you tried putting it in a loop?
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  3. #3
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    Default Re: How to validate user input in a loop

    Yes I tried a while loop like this, but whenever I enter in a double for example. It will go into an infinite loop saying "try again wrong type"

    int i=0;
    while(i<3)
    		{
    		try 
    			{
    		         integerVariable = sc.nextInt();
                             i++;
    			} 
    			catch(InputMismatchException e)
    			{
    		        System.err.println("try again, wrong type");
    			}
    		}
    		}

  4. #4
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    Default Re: How to validate user input in a loop

    If the sc.nextInt() function throws an Exception (which it will if you enter a double), then the i++ line will not be executed.

    Step through this with a debugger, or at least add some print statements, to see what I'm talking about.
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    Default Re: How to validate user input in a loop

    Right, but I thought that it would then eventually reach the top of the while loop and then go back into the try statement.

    I ended up adding sc.next(); in the catch statement and now all is working well.

  6. #6
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    Default Re: How to validate user input in a loop

    Ah, I understand what you meant now.

    The problem is this: nextInt() reads the next integer, which are separated by white space. The enter key counts as white space, so it isn't read in when you call nextInt(). To move the Scanner past the enter character, you have to call next() or nextLine().
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