How to properly exit out of JOptionPanel Exception in thread "main" java.lang.NumberFormatException: null

Question

I am trying to create a GUI where the user has to enter an integer. If the user enters a non-integer, it prompts the GUI. I also want it to exit. When I get it to exit, I get this error:

Exception in thread "main" java.lang.NumberFormatException: null.

I am a bit of a noob and need some guidance :)

public class Generator

{


    public static void main (String[] args)
    { String input = JOptionPane.showInputDialog("Enter Desired Analysis level");
        int analysisLevel = Integer.parseInt(input);
        try
        {
            if (analysisLevel >= 0)
            {
                System.out.println(analysisLevel);

            }


            else
            {

                input = JOptionPane.showInputDialog("Enter Desired Analysis level");

            }
        }
        catch (Exception e)
        {
            System.out.println("Input was no number" + e);
            System.exit(0);

        }
        System.exit(0);
}
}

Answer 1

The problem is that you left the one line that will likely cause an exception (int analysisLevel = Integer.parseInt(input);) out of the try/catch block. You need to move it inside:

String input = JOptionPane.showInputDialog("Enter Desired Analysis level");
try
{
    int analysisLevel = Integer.parseInt(input);
    if (analysisLevel >= 0) {
        System.out.println(analysisLevel);
    } else {
        input = JOptionPane.showInputDialog("Enter Desired Analysis level");
    }
}
catch (Exception e)
{
    System.out.println("Input was no number. " + e);  
}

Additionally you do not need the System.exit(0);'s as the program will exit anyways, and using System.exit(0); is generally not good practice.