for loop finding the prime numbers

Question

I am trying to run this code to print the sum of all the prime numbers less than 2 million. This loop is never ending. Can anyone tell me what is wrong with the code? It see

Answer 1

Here is a complete program of Prime using JOptionPane, i.e. Java GUI

import javax.swing.*;

public class ChkPrime {
    public static void main(String[] args) throws NumberFormatException {
        String str = JOptionPane.showInputDialog(null, "Enter any number: ","Input...", 3);

        try {
            int num = Integer.parseInt(str);


            if (num == 1)
                JOptionPane.showMessageDialog(null, "Your inputed no. " + num + " is not prime.","Error!", 0);

            for(int i = 2; i <= Math.sqrt(num); i++) {
                if(num % i == 0) {
                    JOptionPane.showMessageDialog(null, "Your inputed no. " + num + " is not prime.","Error!", 0);
                    System.exit(0);
                }
            }

            JOptionPane.showMessageDialog(null, "Your inputed no. " + num + " is prime.","Yeh! Got it!", 1);
        }

        catch (NumberFormatException e) {
            JOptionPane.showMessageDialog(null, "Please input numbers...","Error!", 0);
            main(null);
        }
    }
}