After going easily through OCA the material in your OCP book shocked me with the difficulty of installing it into my grey matter.
- Read book thoroughly 2 times.
- Got Ethuware mock exams - results unsatisfactory - around ~60%
- Back to book reading on particularly weak topics and testing the code in IDE - Back to mock exams - now around ~80%
- Exam - 90%.
Would recommend your book - OCP Oracle Certified Professional Java SE 8 Programmer II Study guide by Jeanne Boyarsky and Scott Selikoff as a number 1 (and in my case the only) resource to dig into OCP.
Would also recommend Ethuware mock tests ans they will solidify knowledge gained from the book.