I invested in the full Java 11 study guide by Jeanne Boyarsky and Scott Selikoff (that covers 815 816 817 & 819), and have 2 OCP test vouchers to use, and already passed the Java 8 Associate exam last year.
To make the most of my vouchers I'd like to pass 1Z0-809, and then pass either 1Z0-817 or 1Z0-819 exam. (I've read a comment by Scott Selikoff that 1Z0-817 is easier so it will probably be that one!)
Would I need to buy the OCP 1Z0-809 study guide, or does the book I have cover all the detail needed to pass the 809 exam without having to read the dedicated study guide separately? Of course I understand there will be a lot of duplication, and the APIs may have changed slightly for Java 11, but I hope it's more of a superset of information rather than a rewrite?
Welcome to CodeRanch! Sorry for the late reply, I missed this post.
The 809 is very different than the Java 11 exams. If you choose to use the 816/817 book for the 809, you will need to supplement with other materials. For example, date/time was removed completely from the Java 11 exams which is a whole objective on the 809.