Por cierto corri un ejemplo de JInternalFrame que encontre en la red
import java.awt.event.*;
import java.awt.*;
import javax.swing.JButton;
public class MyInternalFrame extends JInternalFrame {
static int openFrameCount = 0;
static final int xOffset = 30, yOffset = 30;
public MyInternalFrame() {
super("Document #" + (++openFrameCount),
true, //resizable
true, //closable
true, //maximizable
true);//iconifiable
//...Create the GUI and put it in the window...
//...Then set the window size or call pack...
setSize(300,300);
//Set the window's location.
setLocation(xOffset*openFrameCount, yOffset*openFrameCount);
getContentPane().add(new JButton("mari"));
}
}
import javax.swing.JInternalFrame;
import javax.swing.JDesktopPane;
import javax.swing.JMenu;
import javax.swing.JMenuItem;
import javax.swing.JMenuBar;
import javax.swing.JFrame;
import java.awt.event.*;
import java.awt.*;
public class InternalFrameDemo extends JFrame {
JDesktopPane desktop;
public InternalFrameDemo() {
super("InternalFrameDemo");
//Make the big window be indented 50 pixels from each edge
//of the screen.
int inset = 50;
Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
setBounds(inset, inset,
screenSize.width - inset*2,
screenSize.height-inset*2);
//Quit this app when the big window closes.
addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent e) {
System.exit(0);
}
});
//Set up the GUI.
desktop = new JDesktopPane(); //a specialized layered pane
createFrame(); //Create first window
setContentPane(desktop);
setJMenuBar(createMenuBar());
}
protected JMenuBar createMenuBar() {
JMenuBar menuBar = new JMenuBar();
JMenu menu = new JMenu("Document");
JMenuItem menuItem = new JMenuItem("New");
menuItem.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
createFrame();
}
});
menu.add(menuItem);
menuBar.add(menu);
return menuBar;
}
protected void createFrame() {
MyInternalFrame frame = new MyInternalFrame();
frame.setVisible(true);
desktop.add(frame);
try {
frame.setSelected(true);
} catch (java.beans.PropertyVetoException e2) {}
}
public static void main(String[] args) {
InternalFrameDemo frame = new InternalFrameDemo();
frame.setVisible(true);
}
}
hay un tutorial muy bueno de swing en
http://www.programacion.com/java/tutorial/swing/25