I started preparing using Heller & Roberts CJ2CSG book - I don't think it is good enough to be your only resource, as the practice exams are far too weak (and include 1.2 questions) and Collections are not covered well enough.
However, you'll be fine if you also study some of the tutorials you can find online (I used Sun and DeveloperWorks) and the many practice exam questions (try Dan Chisholm's - very hard, but if you can average more than 60% on them the real exam is easy). Reading JavaRanch helps too
