((JComponent) frame.getRootPane().getGlassPane()).setOpaque(false); frame.getRootPane().getGlassPane().setVisible(true);
  public void installUI(JComponent c)  {    if (c instanceof JInternalFrame)      {        frame = (JInternalFrame) c;        ((JComponent) frame.getRootPane().getGlassPane()).setOpaque(false);        frame.getRootPane().getGlassPane().setVisible(true);        installDefaults();        installListeners();        installComponents();        installKeyboardActions();        frame.setOpaque(true);        frame.invalidate();      }  }