Keygen Example

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.*;
import javax.swing.*;

//Credits to Dr0ax@leetcoders.org, for coding the keygen example
@SuppressWarnings("serial")
public class Keygen extends JPanel implements ActionListener{
    JTextField key_field = new JTextField(19);
    JButton generate = new JButton("Generate");
    JButton chk = new JButton("Check key");
    Random r = new Random();

    public Keygen() {
        this.add(key_field);
        this.add(chk);
        this.add(generate);
        generate.addActionListener(this);

        chk.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                String chkStr = key_field.getText();
                String[] parts = chkStr.split("-");
                boolean valid = false;
                //first check: if there are 4 parts total
                if(parts.length != 4)
                    valid = false;
                else{

                    //loop through the four parts of the string
                    outloop: for (int i = 0; i < parts.length; i++)
                    {
                        //second check: break if the part size is not 4 characters total
                        if(parts[i].length() != 4){
                            valid = false;
                            break;
                        }

                        else{
                            //loop through each character of the string
                            for(int x = 0; x < parts[i].length(); x++) {
                                //get the integer value of the char
                                int cv = (int)parts[i].charAt(x);

                                //substract 48 from the number
                                int rndVal = cv - 48;

                                //check the number against the algorithm
                                if (((rndVal >= 0 && rndVal <= 9) || (rndVal >= 17 && rndVal <= 42)) /*|| (rndVal >= 49 && rndVal <= 74)*/  && isPrime(rndVal)) {
                                    valid = true;
                                }
                                else{
                                    //if not valid, set the flag and exit the loop
                                    //you have to use a label (in my case "outloop") because you can't break a nested loop with just the break command
                                    valid = false;
                                    break outloop;
                                }
                            }
                        }
                    }
                }

                if(valid == true)
                key_field.setText("Valid Key!");
                else{key_field.setText("Not a valid key");}
            }
        });
        }


    public static void main(String[] args){
        JFrame f = new JFrame("Keygen Example");
        f.setLocation(100,100);
        f.setDefaultCloseOperation(3);
        f.setSize(250,100);
        f.add(new Keygen());
        f.setVisible(true);
    }

    boolean isPrime(int num){
        int i;
        boolean xD = false;
        for (i=2; i < num ;i++ ){
            int n = num%i;
            if (n==0){
                xD = false;
                break;
            }
          }
          if(i == num)
              xD = true;
          return xD;
    }

    @Override
    public void actionPerformed(ActionEvent arg0) {
        int x = 0;
        int math = 48;
        String nStr = "";
        boolean valid;
        for (int i = 0; i < 19; i++) {
            if(i == 4 || i == 9 || i ==14) {
                nStr += "-";
            }
            else{
                valid = false;
                while(!valid){
                    x = r.nextInt(74) +1;
                    if (/*this makes x only available to hold the ASCII values of the numbers, and uppercase characters ... after you add 48 to it, of course =)*/
                        ((x >= 0 && x <= 9) || (x >= 17 && x <= 42)) && isPrime(x)) {
                        valid = true;
                        math += x;
                        nStr += (char)math;
                        System.out.println(x);
                        break;
                    }
                }
                math = 48;
            }
        }
        key_field.setText(nStr);
    }
}