Other books out there are overly large. They prepare you for the exam, but in a time-consuming way that you don’t really need... if you have some previous Java experience, what’s the point of reading twenty pages about operators?
Source: Is Java Certification Worth It? at Cunningham & Cunningham, Inc.
Job opportunities, promotions, improving your Java skills... know the potential benefits that are reasonable to expect from achieving this certification and also (and perhaps even more important) what you shouldn’t be expecting from it