I would go a little bit further and say that, depending on which language you have your code, you can even use C/C++ to make a bridge between Java and some lang

I would go a little bit further and say that, depending on which language you have your code, you can even use C/C++ to make a bridge between Java and some language interpreter. I've done something like that for integrating a lot of existing python code on a Android app I've done. There's a working sample in my github: https://github.com/joaoventura/pybridge https://github.com/joaoventura/pybridge Performance is pretty good, and the UI is entirely native Android.