Prime Numbers Generation using Java with GUI

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package main;

/**
 *
 * @author markjasongalang
 */
import java.awt.*;
import java.awt.event.*;
import java.util.Locale;
import javax.swing.*;

public class Main implements ActionListener {
    private JFrame frame = new JFrame();
    private JPanel main_panel = new JPanel();
    private JPanel[] mini_panels;
    private JLabel label;
    private JScrollPane sp;

    boolean CheckPrime (int n) {
        boolean prime = true;
        for (int i = 2; i <= (int) Math.sqrt(n); i++) {
            if (n % i == 0) {
                prime = false;
                break;
            }
        }
        return prime;
    }

    Main() {
        frame.setTitle("Sample");
//        frame.setLocationRelativeTo(null);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setResizable(false);

        int n = 640;
        int root = (int) (Math.sqrt(n));
        mini_panels = new JPanel[n];
        main_panel.setLayout(new FlowLayout(FlowLayout.LEADING, 10, 10));
        for (int i = 0; i < n; i++) {
            mini_panels[i] = new JPanel();
            label = new JLabel(Integer.toString(i + 1));
            label.setFont(new Font("ARIAL", Font.PLAIN, 30));
            mini_panels[i].setLayout(new GridBagLayout());
            mini_panels[i].add(label);
            mini_panels[i].setPreferredSize(new Dimension(100, 100));
            if (i + 1 <= 1) {
                mini_panels[i].setBackground(Color.GRAY);
            } else if (CheckPrime(i + 1)) {
                mini_panels[i].setBackground(Color.GREEN);
            } else {
                mini_panels[i].setBackground(Color.YELLOW);
            }
            main_panel.add(mini_panels[i]);
        }
        int size = ((n % 8 == 0 ? n / 8 : n / 8 + 1)) * 110;
        main_panel.setPreferredSize(new Dimension(900, size));
        sp = new JScrollPane(main_panel, JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED, JScrollPane.HORIZONTAL_SCROLLBAR_NEVER);
        frame.add(sp);
        frame.setVisible(true);
        frame.setSize(900, 500);
    }

    @Override
    public void actionPerformed(ActionEvent e) {

    }

    public static void main(String[] args) {
        new Main();
    }
}