Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
 
      if (size.height > screenSize.height)
      {
         size.height = screenSize.height;
      }
      if (size.width > screenSize.width)
      {
         size.width = screenSize.width;
      }
      frame.setLocation((screenSize.width - size.width) / 2, (screenSize.height - size.height) / 2);
      setVisible(true);