There is no doubt that exam simulators play an important role in preparing for any Java certification e.g. OCAJP, OCPJP, OCEJWCD, OCMJEA exams. In fact, they are one of the most important pillars because choosing a good exam simulator with a good book is generally the success mantra of many Java certification aspirants. The exam simulators prepare you well for exams by presenting the the level of questions you can expect in real exams. They provide the must needed practice in exam like environment to gauge your speed and accuracy. I have personally seen difference of 30% in score between people who do a lot of mock exams and who just goes without practicing mock exams. Candidates makes more mistakes when they first took exams and by participating in mock tests, you train your mind to do less mistakes. They also help you to better handle the time pressure of real exam.