Lớp JOptionPane trong Java Swing

public class JOptionPane
   extends JComponent
      implements Accessible

package vn.kienthuclaptrinh.swing;

import java.awt.FlowLayout;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;

public class JOptionPaneExam1 {

    private JFrame mainFrame;
    private JLabel headerLabel;
    private JLabel statusLabel;
    private JPanel controlPanel;

    public JOptionPaneExam1() {
        prepareGUI();
    }

    public static void main(String[] args) {
        JOptionPaneExam1 demo = new JOptionPaneExam1();
        demo.showDialogDemo();
    }

    private void prepareGUI() {
        mainFrame = new JFrame("Vi du JOptionPane trong Java Swing");
        mainFrame.setSize(500, 400);
        mainFrame.setLayout(new GridLayout(3, 1));
        mainFrame.addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent windowEvent) {
                System.exit(0);
            }
        });
        headerLabel = new JLabel("", JLabel.CENTER);
        statusLabel = new JLabel("", JLabel.CENTER);
        statusLabel.setSize(350, 100);
        controlPanel = new JPanel();
        controlPanel.setLayout(new FlowLayout());
        mainFrame.add(headerLabel);
        mainFrame.add(controlPanel);
        mainFrame.add(statusLabel);
        mainFrame.setVisible(true);
    }

    private void showDialogDemo() {
        headerLabel.setText("Control in action: JOptionPane");
        JButton okButton = new JButton("OK");
        JButton javaButton = new JButton("Yes/No");
        JButton cancelButton = new JButton("Yes/No/Cancel");
        okButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                JOptionPane.showMessageDialog(mainFrame, 
                        "Welcome to kienthuclaptrinh.net");
            }
        });
        javaButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                int output = JOptionPane.showConfirmDialog(mainFrame, 
                        "Click any button", "kienthuclaptrinh.net",
                        JOptionPane.YES_NO_OPTION);
                if (output == JOptionPane.YES_OPTION) {
                    statusLabel.setText("Yes selected.");
                } else if (output == JOptionPane.NO_OPTION) {
                    statusLabel.setText("No selected.");
                }
            }
        });
        cancelButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                int output = JOptionPane.showConfirmDialog(mainFrame, 
                        "Click any button", "kienthuclaptrinh.net",
                        JOptionPane.YES_NO_CANCEL_OPTION, 
                        JOptionPane.INFORMATION_MESSAGE);
                if (output == JOptionPane.YES_OPTION) {
                    statusLabel.setText("Yes selected.");
                } else if (output == JOptionPane.NO_OPTION) {
                    statusLabel.setText("No selected.");
                } else if (output == JOptionPane.CANCEL_OPTION) {
                    statusLabel.setText("Cancel selected.");
                }
            }
        });
        controlPanel.add(okButton);
        controlPanel.add(javaButton);
        controlPanel.add(cancelButton);
        mainFrame.setVisible(true);
    }
}