After 5 years away from programming I just passed OCA Java 8 with 85%
It took me about 40-50 days almost full day(5-8 hours per day) studying
I basically studied only from the Jeanne boyarsky and scott selikoff
OCA: Oracle Certified Associate Java SE 8 Programmer I Study Guide: Exam 1Z0-808
I did the tests at the end of each chapter and after a while I bought
OCA / OCP Java SE 8 Programmer Practice Tests and i did the firsts chapters.
I did write some java code. Small programs usually less than 100 lines of code only on things that i found difficult to understand or remember.