import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.UIManager;


public class PrimerNumber {

    private static final long[] primes = new long[61521918];//new long[(int) (Runtime.getRuntime().maxMemory()/11)];
    static {
        System.out.println(primes.length);
        primes[0] = 2;
        primes[1] = 3;
        primes[2] = 5;
        //these are known and needed in the beginning
    }

    private static int idx = 3; //already assigned 3 primes

    public static void main(String[] args){
        Runtime.getRuntime().addShutdownHook(new Thread(){ //to be run when program exits
            public void run(){
                System.out.print("\nCalculated " + idx + " primes\n" + idx + "th prime: " + primes[idx - 1]);
            }
        });
        try {
            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName()); //set UI to Windows/Mac/Linux (whatever native UI is)
        } catch (Exception useless){}
        final JFrame frame = new JFrame();//frame for gui
        frame.setUndecorated(true);//no buttons in pane
        final JButton button = new JButton("Exit");
        button.addActionListener(new ActionListener(){//when Exit button clicked
            public void actionPerformed(ActionEvent e) {
                frame.setVisible(false);
                frame.dispose();
                JOptionPane.showMessageDialog(null, "\nCalculated " + idx + " primes\n" + idx + "th prime: " + primes[idx - 1]);
                System.exit(0);
            }
        });
        frame.add(button);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(500, 500);
        frame.pack();
        frame.setLocationRelativeTo(null);//center frame
        frame.setVisible(true);
        while(frame.isVisible()){
            System.out.println(calculateNextPrime());
        }

    }

    private static long calculateNextPrime(){
        if(idx == primes.length){
            System.out.println("\nCannot calculate more prime numbers (reached max memory usage).");
            System.out.print("Last prime calculated: ");
            System.exit(0);
            return primes[idx - 1];
        }
        primeSearch:
            for(long i = primes[idx - 1] + 2;; i += 2){ //use last prime as a starting point, but add 2 so it stays odd
                for(int j = 0; j < idx; j++){
                    if(i % primes[j] == 0){ //check if any of the previous primes are a factor of current number
                        //if no previous primes are a factor, then current number is a prime
                        continue primeSearch;
                    }
                }
                //if execution reaches here, no previous are a factor, so set the next prime number and increase index
                return primes[idx++] = i;
            }
    }

}