macOS Beginner questions

Hey guys, I just bought a mba few months ago and got somewhat familiar with it. It's my first mac. Currently im in school for computer engineering and focusing more towards software. I figured since i got the mac that i could spend my summer trying to learn writing code for it using Xcode. So far i know some basic c++ and java. I was reading up on coding for macs and bought a book called "Cocoa Programming Developer's Handbook" by David Chisnall. I choose this book because i saw it used Xcode and written for people that know some programming. The other objective c books i saw took it as the reader knew nothing about programming so it seemed like i knew half of the book already. Since this book is cocoa programming should i have also bought an objective c book as well? and any recommendations of books that briefly go over the basics and teach towards more advanced areas. Thanks for any helpful replies.

thanks