I don't know how relevant it is for mobile development but I'd recommend Effective Java by Joshua Bloch (http://www.amazon.com/Effective-Java-2nd-Joshua-Bloch/dp/032...). It's essentially the equivalent of Effective C++ for Java and it does a good job of explaining how to properly use the language. It also contains quite a few general programming advises which are applicable to other languages. Just keep in mind that it assumes that you already know the language and have a bit of experience under your belt.