The vast majority of Android applications are written in Java. In order to truly reverse engineer Java code, one should generally be able to engineer Java code first. Teaching Java is well beyond the scope of this book. We will, however, show a few useful reversing methods that we think will be useful and can be done by an average mobile forensic examiner. Many hundreds of tutorials and guides have been written online for Android reversing, from the very basic to the highly advance.
Anyone looking for more information on the subject should easily be able to find what they are looking for. As always, www.xda-developers.com is an incredibly useful resource, and entire books have been dedicated to the subject. There is also an incredibly detailed, updated list of tools by Ashish Bhatia that can be found at https://github.com/ashishb/android-security-awesome.