We teach both object and functional approaches in the book, but we do not immediately jump into functional coding until a little way into the book. This is because we need to make sure that you first have a grounding in the basics of the language, such as types, variables and so on. But functional coding is one of the most powerful features in the language, and we make sure that you have a good understanding of not simply how to process collections with functional code, but also how to create higher-order functions (functions which accept functions and return functions) so that you can do things like compose data converters together.
Hope this helps.
Head First Android Development