🚀 go-pugleaf

Hi,
Could someone provide me with  sample code to prevent users from opening
or instatiating a window that is already open or instantiated??. Thanks
a lot!!

The code I am using now  is as follows:

  void jButton1_actionPerformed(ActionEvent e) {
    StandOrdListFrame frame = new StandOrdListFrame();
    boolean packFrame=false;

    if (packFrame)
      frame.pack();
    else
      frame.validate();
    Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
    Dimension frameSize = frame.getPreferredSize();
    if (frameSize.height > screenSize.height)
      frameSize.height = screenSize.height;
    if (frameSize.width > screenSize.width)
      frameSize.width = screenSize.width;
    frame.setLocation((screenSize.width - frameSize.width) / 2,
(screenSize.height - frameSize.height) / 2);
    frame.setVisible(true);
  }