One of the things you are getting in a book by Bill and I is a text by people who are not just knowlegable on the subject but experts on the exam itself. It is possible to know
Java but not to know a great deal on the specifics of the exam.
I almost never go onto the web without reading the JavaRanch programmer certification forums and I have received thousands of emails from people who have taken the exam.
As Bill has mentioned, the book concentrates on just the exam material so, as the title indicates it is ideal for cramming on only the relevant subjects.