1) Horstman Volume 1 is just a run through the eyes, personally for me he is so-so. Stupid guide, does not explain anything. In the case of the Shield a little better, but in principle the same
2) I advise to take a book to prepare for the exam OCA Java SE 8 Programmer I, the author seems Boyarsky, on torrents is:) It is explained quite well, better than in the horstman, consider it not as a book for the exam).It is really well written and gives a definite understanding of how everything works in Java
3) There is a video course on preparing for the exam from a very cool dude, also called. The speaker is very good, just follow the sections of the book and his video lectures
4) Once you have that figured out, read Effective Java - 2nd edition, although old, is still considered the best literature on Java
All of the above, except Horstman, requires not much, but knowledge of English. In general, good luck :) The main thing is not to spend too much time on the horstman and shield, to me, so it's more a guide than a manual. They do not give an understanding of the language