It is absolutely necessary to purchase both books, although my opinion might be slightly biased.
The study guide contains about 150 sample SCJA questions, with questions at the end of each chapter, three small mock exams of 20 questions each at midway points through the book, and a final mock exam of 50 questions that simulates the real exam.
The second book is what most people use to really polish off their knowledge and build the confidence they need to get a really high score on the exam. It contains 350 questions, different from the questions in the SCJA Study Guide, that really hit the exam objectives from just about every imaginable angle.
Hi Preetha, you can go through objectives for the exam on sun's site and you can also go through SCJA FAQS here on javaranch. That will give you a start. For Java language, you can refer book by Kathy Sierra. For UML you can refer to the free pdf available on www.hfoobook.com and it would be better if you can buy Cameron Mckenzie's books, otherwise there are other resources online which aren't specifically for SCJA preparation. Also join the google group for SCJA http://groups.google.co.in/group/scja_sun?hl=en Thanks.
Swapnil S. Sonawane<br /> <br />B.Tech (Expected May 2009)<br />Computer Science, NIT Durgapur, India<br />SCJA 1.0