I think you should go for at least one of them....I myself was of the confidence that you don't need any mock exams. But I realized that you will not get good marks even you know everything. There are some gotchas and traps that you will come to know only after giving some mock papers. You will also get familiar with the format of questions on the exam. I think that everyone should give mock exams more than wasting time on reading books over and over again like I did....
Welcome to JavaRanch. You can find a lot of useful information, including a list of mock exams, in the JavaRanch SCJP FAQ.
Please use real words when you post in the forums here. Single letters like "n i m" and "d" are not real words and are hard to understand for some people. [ September 06, 2008: Message edited by: Jesper Young ]