Catch blank variable int input in java

Question

I want my code to catch if the user didn't input anything. I can't use ab.equals(null), ab.isEmpty() because I convert the String to integer as you can see.

import javax.swing.JOptionPane;
public class Mango {


    public static void main (String[] args){

        String ab = JOptionPane.showInputDialog("Enter Anything");
        double sum = 0;
        double x = Integer.parseInt(ab);

        if(x <= 0){

            System.out.println("Empty!");

        }else{

            sum+=x; 

        }
    }

Answer 1

Check the return value BEFORE you try converting it...

String ab = JOptionPane.showInputDialog("Enter Anything");
if (ab != null && !ab.trim().isEmpty()) {
    // Try and convert the value...
} else {
    // Bad input
}

Example

double sum = 0;
String ab = JOptionPane.showInputDialog("Enter Anything");
if (ab != null && !ab.trim().isEmpty()) {
    double x = Integer.parseInt(ab);
    sum += x;
} else {
    System.out.println("\"" + ab + "\" is not a valid input value");
}