Hello,
    I am creating a program where I have differnt JInternalFrame classes
and I would only like 1 frame per class to be displayed at a time.
Example is having a cardfile frame and a sales frame open at the same
time but not be able to create another cardfile frame if one is already
opened. Below is the code to set up a generic JDesktop and one JInternal
frame. If someone knows how to do this thanks in advance.

InternalFrameDemo.java

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());

        //Make dragging faster:
        desktop.putClientProperty("JDesktopPane.dragMode", "outline");
    }

    protected JMenuBar createMenuBar() {
        JMenuBar menuBar = new JMenuBar();

        JMenu menu = new JMenu("Document");
        menu.setMnemonic(KeyEvent.VK_D);
        JMenuItem menuItem = new JMenuItem("New");
        menuItem.setMnemonic(KeyEvent.VK_N);
        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); //necessary as of 1.3; OK to use before
        desktop.add(frame);
        try {
            frame.setSelected(true);
        } catch (java.beans.PropertyVetoException e) {}
    }

    public static void main(String[] args) {
        InternalFrameDemo frame = new InternalFrameDemo();
        frame.setVisible(true);
    }
}

MyInternalFrame.java - allow only 1 MyInternal Frame open per instance
but I will have another class called MyInternalFrame2 and would like it
possible to have one each open per instance.

import javax.swing.JInternalFrame;

import java.awt.event.*;
import java.awt.*;

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);
    }
}