The structure of the classes.dex file is published by Google. You can find the complete specification at https://source.android.com/devices/tech/dalvik/dex-format.html. You can see a simple schematic of the file format in Figure 2-1.
An excellent way to do your own deep dive into the classes.dex format is to use some sort of classes.dex viewer such as the one provided by the 010 Editor. You’ll need to follow these steps:
1. Unzip an APK by renaming the extension to zip and then unzipping. If you can’t find one, check the online source code for this chapter.
2. Open classes.dex ...