How to Dialog appear with look & feels CrossPlatform?

[Thang Nguyen Cao]

Why this follow code don't appear with L&Fs CrossPlatform?It's still appear with the title bar of OS that I use ( Windows XP).

package myprojects.icondialogswing;

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

/*
* IconDialogSwing.java
*
* Created on November 6, 2004, 12:07 AM
*/

/**
*
* @author thangcan
*/
public class IconDialogSwing extends JPanel {
ImageIcon icon = createImageIcon("icon/middle.gif");
JFrame frame;
String iconDesc = "A JOptionPane has its choice of icons";
/** Creates a new instance of IconDialogSwing */
public IconDialogSwing() {
super(new BorderLayout());

JPanel iconPanel = createIconDialog();
JLabel label = new JLabel("Click the \"Show it!\" button"
+ " to bring up the selected dialog.",
JLabel.CENTER);

iconPanel.setBorder(BorderFactory.createEmptyBorder(20,20,5,20));

this.add(iconPanel,BorderLayout.PAGE_START);
this.add(label,BorderLayout.PAGE_END);
this.setBorder(BorderFactory.createEmptyBorder(10,10,10,10));
}

protected static ImageIcon createImageIcon(String path) {
java.net.URL imgURL = IconDialogSwing.class.getResource(path);
if (imgURL != null) {
return new ImageIcon(imgURL);
} else {
System.err.println("Couldn't find file: " + path);
return null;
}
}

private JPanel create2ColPane(String description,
JRadioButton[] radioButtons,
JButton showButton) {
JLabel label = new JLabel(description);
int numPerColumn = radioButtons.length/2;

JPanel grid = new JPanel(new GridLayout(0, 2));
for (int i = 0; i < numPerColumn; i++) {
grid.add(radioButtons);
grid.add(radioButtons[i + numPerColumn]);
}

JPanel box = new JPanel();
box.setLayout(new BoxLayout(box, BoxLayout.PAGE_AXIS));
box.add(label);
grid.setAlignmentX(0.0f);
box.add(grid);

JPanel pane = new JPanel(new BorderLayout());
pane.add(box, BorderLayout.PAGE_START);
pane.add(showButton, BorderLayout.PAGE_END);

return pane;
}

private JPanel createIconDialog() {
JButton showItButton = null;

final int numButtons = 6;
JRadioButton[] radioButtons = new JRadioButton[numButtons];
final ButtonGroup group = new ButtonGroup();

final String plainCommand = "plain";
final String infoCommand = "info";
final String questionCommand = "question";
final String errorCommand = "error";
final String warningCommand = "warning";
final String customCommand = "custom";

radioButtons[0] = new JRadioButton("Plain (no icon)");
radioButtons[0].setActionCommand(plainCommand);

radioButtons[1] = new JRadioButton("Information icon");
radioButtons[1].setActionCommand(infoCommand);

radioButtons[2] = new JRadioButton("Question icon");
radioButtons[2].setActionCommand(questionCommand);

radioButtons[3] = new JRadioButton("Error icon");
radioButtons[3].setActionCommand(errorCommand);

radioButtons[4] = new JRadioButton("Warning icon");
radioButtons[4].setActionCommand(warningCommand);

radioButtons[5] = new JRadioButton("Custom icon");
radioButtons[5].setActionCommand(customCommand);

for (int i = 0; i < numButtons; i++) {
group.add(radioButtons);
}
radioButtons[0].setSelected(true);

showItButton = new JButton("Show it!");
showItButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
String command = group.getSelection().getActionCommand();

//no icon
if (command == plainCommand) {
JOptionPane.showMessageDialog(frame,
"Eggs aren't supposed to be green.",
"A plain message",
JOptionPane.PLAIN_MESSAGE);
//information icon
}
else if (command == infoCommand) {
JOptionPane.showMessageDialog(frame,
"Eggs aren't supposed to be green.",
"Inane informational dialog",
JOptionPane.INFORMATION_MESSAGE);
//question icon
}
else if (command == questionCommand) {
JOptionPane.showMessageDialog(frame,
"You shouldn't use a message dialog "
+ "(like this)\n"
+ "for a question, OK?",
"Inane question",
JOptionPane.QUESTION_MESSAGE);
//error icon
}
else if (command == errorCommand) {
JOptionPane.showMessageDialog(frame,
"Eggs aren't supposed to be green.",
"Inane error",
JOptionPane.ERROR_MESSAGE);
//warning icon
}
else if (command == warningCommand) {
JOptionPane.showMessageDialog(frame,
"Eggs aren't supposed to be green.",
"Inane warning",
JOptionPane.WARNING_MESSAGE);
//custom icon
}
else if (command == customCommand) {
JOptionPane.showMessageDialog(frame,
"Eggs aren't supposed to be green.",
"Inane custom dialog",
JOptionPane.INFORMATION_MESSAGE,
icon);
}
}
});

return create2ColPane(iconDesc + ":",
radioButtons,
showItButton);
}

private static void createAndShowGUI() {
JFrame.setDefaultLookAndFeelDecorated(true);

JFrame frame = new JFrame("IconDialogSwing");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

IconDialogSwing newContentPane = new IconDialogSwing();
newContentPane.setOpaque(true); //content panes must be opaque
frame.setContentPane(newContentPane);

frame.pack();
frame.setVisible(true);
}

public static void main(String[] args) {
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGUI();
}
});
}
}


Though I inserted a snip code setDefaultLookAndFeelDecorated(true).Why 's that???
When I wrote a app that extends JDialog, I also used method setContentPane(contenPane) which contentPane = new JOptionPane(...) and method setDefaultLookAndFeelDecorated(true), this app appear with L&Fs CrossPlatform?
Help me.