I passed OCP 8 exam with 90 % . Took me around 3 months to prepare for it . Two things that immensely helped me in achieving this are
OCP: Oracle Certified Professional Java SE 8 Programmer II Study Guide: Exam 1Z0-809
I want to thank the authors Jeanne Boyarsky and Scott Selikof , for the great book .
also ETS team for making a test series that so closely resembles the actual test scenario. Eventhough my average scores in ETS mocks were around 70% , i was confident that in actual test i can push it up a little:)
My advice for future test takers is to focus on each and every test objectives .