If you figure out how to get JDEE working with Emacs 24, then you will be my personal hero.
I've tried everything possible to get it working, and it always bombs out with a message saying "Error: Forgot to expand macro eieio-object-p" in the *Compile-Log* buffer and "Invalid function: eieio-object-p" in the *Warnings* buffer. CEDET
seems to be the problem (or at least how JDEE uses CEDET). I've even tried the latest CEDET bzr snapshots
and that didn't help (it caused errors of another kind).
My solution was to download the source for Emacs 23.4.1 and compile that, since at least that works with JDEE. Unfortunately it looks like there hasn't been much activity on JDEE lately, so I have no idea if it will be fixed for Emacs 24 any time soon.
It's a shame, because JDEE makes Emacs pretty decent for Java development (magnitudes better than the normal built-in Java mode).