Add JInternalFrame to JDesktopPane in execution time

I have a problem with a JDesktopPane, I add JInternalFrame on it and then show it on a JFrame.

The problem is when I try to add another JInternalFrame in execution time.

I use the same method to add the same JInternalFrame but its dosnt shows up.

public class Desktop extends JDeskto开发者_如何学JAVApPane {
    (...)
    public void addJInternalFrameBox(JInternalFrameBox jifb) {
     this.add(jifb, desktop.CENTER_ALIGNMENT);
     this.repaint();
     this.validate();
    }
}

JInternalFrameBox class:

public class JInternalFrameBox extends JInternalFrame {
    (...)
    public JInternalFrameBox(Integer id) {
        this.id = id;
        setUpFrame();
    }
    public void setUpFrame() {
        JLabel lbl = new JLabel("test");
        lbl.setVisible(true);

        this.add(lbl);
        this.setPreferredSize(INTERNAL_FRAME_SIZE);
        this.setLocation(100, 100);
        this.setIconifiable(true);
        this.setClosable(true);
        this.pack();
        this.setVisible(true);
    }
}    

jButtonBox the button that open the JInternalFrameBox:

public class jButtonBox extends JButton implements MouseListener {
    public void mouseReleased(MouseEvent e) {
        JInternalFrameBox jifb = new JInternalFrameBox(id);
        jifb.setVisible(true);
        Desktop df = Desktop.getInstance();
        df.addJInternalFrameBox(jifb);
    }
    (...)
}

Read the section from the Swing tutorial on How to Use Internal Frames for a working example.

Don't use a JPanel for your desktop, but rather use a JDesktopPane. That's specifically what its for.

you have to set both location and size of the internal frame, as in

    setSize(INTERNAL_FRAME_SIZE); // instead of setPref
    setLocation(100, 100);

hm ... maybe not (just saw the pack in your code) - no more guessing without an sscce, as others already stated