Android has many components and is not analogous to Java. At the lowest level Android runs on top of Linux and has drivers, services, etc. This is a very important part of Android that most books and most developers miss. Of course our book covers how to work with Android at this level as well :-) As for Java the orignal Android developers decided to use the Java language as the core language for the application tier of Android and developed their own Java Virtual Machine called the Dalvik Virtual Machine https://secure.wikimedia.org/wikipedia/en/wiki/Dalvik_%28software%29. It has its own peculiarities, for example its register based not stack based, but it is highly optimized for the resource constrained environments of phones. I hope hat helps some but the book covers these differences in much greater depth.