Apart from books, exam simulators are another essential tool to prepare for Java certifications. They not only give you the opportunity to test you knowledge topic wise but also provide the helpful explanation to clear your doubt and misconception, which means you can learn on the fly. Actually, when I prepared for my SCJP exam, I learned a lot of new concept by just giving mock exams and solving practice question. Since most of the Java certification aspirants are Java developer with some experience i.e. they have done a good amount of coding, they can easily understand the code but they might not be familiar with exam format.
Some of you might ask, Why software project manager should read books? Isn't they are experienced enough to become a project manager and handle software development? A genuine question but Software management is harder than any other management purely because every software is different than the previous one. Many other streams of engineering e.g. Civil or Mechanical got better in terms of estimation and management with the help of software but software development is still run on experience.