Crear VEntanas Internas En Java

Crear Ventanas Internas en Java
Aquí les dejo la clase por la cual podemos crear ventanas internas utilizando el lenguaje JAVA.
import java.awt.BorderLayout;
import java.awt.Dimension;
importjava.awt.Graphics;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import java.util.Random;
import javax.swing.JFrame;
import javax.swing.JDesktopPane;
importjavax.swing.JMenuBar;
import javax.swing.JMenu;
import javax.swing.JMenuItem;
import javax.swing.JInternalFrame;
import javax.swing.JPanel;
import javax.swing.ImageIcon;

public class DesktopFrameextends JFrame
{
private JDesktopPane theDesktop;

// set up GUI
public DesktopFrame()
{
super( "Uso del Panel del Escritorio" );

JMenuBar bar = new JMenuBar(); //create menu bar
JMenu addMenu = new JMenu( "Añadir" ); // create Add menu
JMenuItem newFrame = new JMenuItem( "Ventana Interna" );

addMenu.add( newFrame ); // add new frameitem to Add menu
bar.add( addMenu ); // add Add menu to menu bar
setJMenuBar( bar ); // set menu bar for this application

theDesktop = new JDesktopPane(); // create desktop paneadd( theDesktop ); // add desktop pane to frame

// set up listener for newFrame menu item
newFrame.addActionListener(

new ActionListener() // anonymous innerclass
{
// display new internal window
public void actionPerformed( ActionEvent event )
{
// create internal frameJInternalFrame frame = new JInternalFrame(
"Internal Frame", true, true, true, true );

MyJPanel panel = new MyJPanel(); // create new panelframe.add( panel, BorderLayout.CENTER ); // add panel
frame.pack(); // set internal frame to size of contents

theDesktop.add( frame ); // attach internal frame...