The new fourth edition of Barron's Advanced Placement Computer Science test preparation manual has been updated with a new case study. This new GridWorld Case Study will be tested on the AP exam starting in May 2008. The manual presents four full-length AP practice exams, two each for Levels A and AB. Two of these exams are presented as diagnostic tests, with charts detailing the topics for each question. All four model tests have questions answered and explained. Prospective test takers will also find an extensive subject review, starting with a review of Java 5.0 and going on to cover all topics questioned in both the Level A and Level AB exams. There are new sections on storage of numbers and random numbers.