Turns out, with an android target of 23 or older my approach is more than fine. But google decided to make it more complicated going forwards. As 23 is no longer viable version for updates.

So, I read through the block post (multiple times), extracted everything I needed and managed to cram everything into one java file.

also I get this warning:

WARNING: Configuration 'compile' is obsolete and has been replaced with 'implementation' and 'api'.
It will be removed at the end of 2018. For more information see: http://d.android.com/r/tools/update-dependency-configurations.html

since it's now April 2019 I'm going to ignore that until it bites me in the back ;-)

All in all I'm once again reminded why I'm not a fan of Java....

Thanks @VRonin and @ekkescorner , for helping me solve this, very much appreciated.