I have taught it in every possible configuration, and yes you *could* get somewhere in four 4-hour classes as long as you really pick your topics. For example, don't do ALL loops, maybe just a *for* loop. Don't go into every detail about every operator... do they really need bit-shifting? And pick just a few Swing components, and use inner classes in the context of even-handling, and you could have some fun.
I'd much prefer the way Thomas is doing it -- with that much time, and spread out like that. At Sun, it was always 40 hours of teaching, but in five consecutive days! There is just not enough time for them to absorb it before moving on to the next topics, so they really walk out with a lot less capability than if the same 40 hours were spread out. Or even less capability than if they had 20 hours, but spread out (and with a little homework).
For a short duration class like that, do you have a chance to give them prerequisite reading or self-evaluations before coming to the class? So that you at least know they all meet *some* basic requirement and you aren't getting C++ programmers and HTML-only folks in the same room on day one. In which case, you'll need a good plan to handle them both
(I know we've all been there in one way or another with students)
cheers,
Kathy