I just want to share my experience during my review for the Java OCA and OCP certification exams.
First for the OCA, it took me around 3 months with an average of 2 - 4 hrs review per day (due to my work) in order to be prepared. I followed Jeanne and Scott's OCA Study Guide and it really helped me a lot in understanding concepts such as polymorphism, method overridding / overloading / hiding, object references etc. Their review questions were a lot tougher than the actual exam (because of the "choose all that apply" term) and most of the questions there are really tricky which I think was intended to get to use to the actual exam questions.
For those who are planning to take the certification also, the following are my mock exam results from the study guide which I think of should be a good reference for you if you also reading their book.
For the OCP, It also took me around 3 months with 2 - 4 hrs per day to get prepared for the exam. I have to admit that the OCP exam was far tougher than the OCA exam because of the broad topics and the inclusion of functional programming using lambdas and stream api. During my review, I followed the OCP Guide of Jeanne and Scott. They really explained well all the concepts that I need to know especially for streams and concurrency. The only thing that annoys me during the review is that, I really need to memorize too many methods / concepts because I'm not good at memorizing at all. What I did is that, I apply all the concepts and knowledge I've learned in the real work and it turns out that it is easier for me to grasps the idea as oppose to just memorizing it. But still, I have to memorize some of the important methods such as Path and Files api of NIO.
The following are the results of my mock exam in the OCP Study Guide (note that this is the second time I take the mock exam because I did not record my first attempt).
Of course I was aiming for at least 90% average on each of the exam because this is my second attempt and yet was unable to do so. That's when I started to search for some mock exams online and I found that the Enthuware mock exams have so many good reviews that I decided to buy it. With Enthuware, you will have that kind of feeling that you are really taking the actual exam. I mean, it really is because of the functionality like marking the question to be reviewed it again after some time, striking wrong answers, review all questions etc. I also found out that there were some many important topics covered there especially for JDBC. They explained well in detail the correct answer and why that the other answers are wrong.
I study enthuware for about 2 weeks and the following are my first attempt exam results:
Test 1: 86%
Test 2: 76%
Test 3: 86%
Test 4: 91%
Test 5: 79%
Last Day Test: 76%
Actual Exam Result: 95%
So for me, if you study hard and follow the study guide of Jeanne and Scott tandem it with Enthuware Mock Exams will really help you in passing either the OCA or the OCP exam.
My tip for those who are currently reviewing for the exam is that, you should understand the concepts really well, practice detecting failing codes, and try to at least answer every questions within 1 to 1.5 minutes.