I don't have a puzzle of my own today - I've covered up most things I know & I really don't want to end up repeating myself! So for now I am going to point you to a puzzle I had come across some time ago - http://code-o-matic.blogspot.com/2009/02/crazy-java-puzzler.html
I really don't know the answer to this puzzle - but then again I've never been good with Generics or hardcore Java - you folks might know an answer. Give it a shot - and do let us know too if you got an answer!