NetBeans GUI, other layouts

package temp;

import java.awt.Color;
import java.util.Random;

public class Main extends javax.swing.JFrame {

    /** Creates new form NewJFrame */
    public Main() {
        initComponents();
    }

    /**
     * This method is called from within the constructor to
     * initialize the form. WARNING: Do NOT modify this code.
     * The content is always regenerated by the Form Editor.
     */
    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">
    private void initComponents() {

        colorPanel = new javax.swing.JPanel();
        buttonPanel = new javax.swing.JPanel();
        changeButton = new javax.swing.JButton();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        setBackground(new java.awt.Color(0, 255, 255));
        getContentPane().setLayout(new javax.swing.BoxLayout(getContentPane(),
            javax.swing.BoxLayout.PAGE_AXIS));

        colorPanel.setBackground(new java.awt.Color(255, 0, 255));
        colorPanel.setPreferredSize(new java.awt.Dimension(320, 240));
        getContentPane().add(colorPanel);

        buttonPanel.setBackground(new java.awt.Color(0, 255, 255));
        buttonPanel.setPreferredSize(new java.awt.Dimension(320, 120));
        buttonPanel.setLayout(new java.awt.GridBagLayout());

        changeButton.setText("Change Colors");
        changeButton.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                changeButtonActionPerformed(evt);
            }
        });
        buttonPanel.add(changeButton, new java.awt.GridBagConstraints());

        getContentPane().add(buttonPanel);

        pack();
    }// </editor-fold>

    private void changeButtonActionPerformed(java.awt.event.ActionEvent evt) {
        colorPanel.setBackground(new Color(r.nextInt()));
        buttonPanel.setBackground(new Color(r.nextInt()));
    }

    /**
    * @param args the command line arguments
    */
    public static void main(String args[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new Main().setVisible(true);
            }
        });
    }

    private static final Random r = new Random();
    // Variables declaration - do not modify
    private javax.swing.JPanel buttonPanel;
    private javax.swing.JButton changeButton;
    private javax.swing.JPanel colorPanel;
    // End of variables declaration
}