the best book i've seen so far is java black book, that explains java....don't suddenly think you'll pick up android over a weekend, I've been learning java for 6 months and still feel I don't know anything, some people go learning java for 2 years....I recommend going for java so that you run your knowledge more.you'll learn more about it.
Let me summarise a few things for you so you understand java better.
Java is like Russian dolls, statements and expressions, make the methods and objects possible for the classes.
that's the golden rule. you must read the code downwards, you will learn about strings, string concatenations, case sensitivty, and variables, and a dozen other things. Don't be daunted though.
You could literally read 200 pages of 'sams teach yourself java' and you'll be more than ready to understand code!
look at it this way.
If you learn Javascript alongside Java - you'll understand more about how javascript creates it's own variables, while you rely in Java on pre-made variables from the libraries.
get reading, you won't regret it.
happy coding!