Is it possible to learn several programming languages ​​at the same time?

Question

Java

Now I work as a novice Android developer, I work, slowly it turns out.
But there was a great desire to learn Objective-C for IOS development and cocos 2D. Should I start reading books on Objective-C now? Won't it give me headaches and make me "stupid" when coding in Java?
Is it better to wait a couple of months - half a year, when I will study Java sanely and then start reading about Objective-C, or start now, does one interfere with the other?
P.s. I found this cool book macscripter.ru/uploads/files/BecomeAnXcoder.Russian.pdf