> I'm not sure if I want to subclass the existing jspinner and add another button to the right which will invoke my panel,
unless you want to use the spinner buttons to increment/decrement the spinner value without your panel showing,
you could remove the existing listeners from the spinner buttons, then use those buttons to trigger your panel showing,
instead of adding another button.
the above may depend on the L&F used.
> Bits which may or may not be difficult are when the panel overlaps the edge of the frame and does not fit on the desktoppane
I would have thought your panel would show in a popup, and
java would/should/possibly does (?) handle that situation.
another possibility is to use a JComboBox with its built-in popup
a simple example is here
http://www.java.happycodings.com/Java_Swing/code15.html