To develop add-ins for Android, you can use either C++ or Java Native Interface.
The add-in development result is a set of dynamic libraries (*.so) for all supported CPU architectures. If you use Java code, the result must also include an .apk file. The .apk file is not a standalone application, it is not intended for running on its own. It is included in the mobile application package.
See the project example in directory \example\NativeAPIMobile\Android_Proj\.
To debug an add-in, you can also use the option to load dynamic libraries from web publications. The libraries are loaded automatically after you update a configuration (with those libraries included) on a mobile device from a web publication on a developer computer.