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Thread: How to make Java determine if a values is an integer or not.

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    Angry How to make Java determine if a values is an integer or not.

    In my code I'm trying to test if a value is an integer or not. If the entered value is an integer, than I let the user proceed; However, If it isn't the user must go back and enter a valid value. I have no idea what syntax or methods I need to use to make this work. In visual basic I know it's something like "TryParse" but I'm sure it's different in Java. Any Ideas?


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    Default Re: How to make Java determine if a values is an integer or not.

    You could always try this:
    int number;
    int number2;
    Scanner console = new Scanner(System.in);

    try
    {
    number = console.nextInt();
    // OR if using JOptionPane
    number2 = Integer.parseInt(JOptionPane.showInputDialog(null, "Enter an integer.", "Enter an integer.", JOptionPane.PLAIN_MESSAGE));

    }

    catch(InputMismatchException imeRef)
    {
    String str = console.next();
    System.out.println("Invalid.");
    }

    // OR if using JOptionPane

    catch(NumberFormatException nfeRef)
    {
    JOptionPane.showMessageDialog(null, "Invalid.");
    }

    NOTE: the two int numbers are alternate examples. InputMismatch is for console and NumberFormatException is for JOptionPane.
    Don't use both numbers. Also, you may need a while loop and a boolean that will be set to true if the Exception is not caught and originally the boolean is false and therefore, as long as it's not an int, it will keep asking.

    I know for InputMismatchException, you have to clean out the invalid results, which is what I did with that String thing in the catch block.

    I can't recall if you'd need to reset it for NumberFormatException.
    Last edited by javapenguin; August 17th, 2011 at 05:50 PM.

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    Default Re: How to make Java determine if a values is an integer or not.

    You don't provide any code, so the question is a bit out of context. Do you mean you need to check if a String is a valid int? Then you can a) loop over all the chars and check if each one matches 0-9, b) Use Integer.parseInt in a try/catch - if no exception is thrown its valid, if an exception is thrown it is not valid.

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    Default Re: How to make Java determine if a values is an integer or not.

    c) Use a regular expresion
    Improving the world one idiot at a time!

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    Default Re: How to make Java determine if a values is an integer or not.

    If the entered value is an integer
    <autism>Integer.parseInt() and Scanner.nextInt() test if the entered value is a Java int actually, but Java ints are a subset of integers.</autism>
    java.math.BigInteger(String) can do it.

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    MiniatureBeast (August 18th, 2011)

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    Default Re: How to make Java determine if a values is an integer or not.

    Thanks I'll look into this. Thanks to everyone else as well

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