You can set it to be undecorated and provide your own, in which case you
have full access.  That's probably more than you want to do.

Otherwise, you probably need to be more clear about what you want to do
via your mouse listener.  For enter/exit actions, you may be out of
luck.  For movement, you can use other listeners to respond after your
JFrame is moved, resized, etc.

= Steve =

You could try setting up a MouseListener on JFrame as a whole and only
pay attention to events with y < 26.

If that does not work you could try tapping in at a lower level.  See
http://mindprod.com/jgloss/event11.html for how.