I suggest you to follow "Java 2 Sun Certified Programmer & Developer for Java 2" the "2-in-1 Exam Study Guide" by "Kathy Sierra and Bert Bates". This is the best one. And ofcourse better you buy any simulator from either Whizlabs or Enthuware and work on mock tests.
In fact the original exam is easy than these mock
test, so that you will get more confidence on real exam.
Hope this helps.