Code written in Oak still works in Java 14. You can still write `public abstract interface BlaBla{}` and it still works. If it doesn't work (due to reflection safety changes in Java9), it sill surely compile with newer compiler.

Another thing, are tools used to compile still available? I tried to compile my BCS Android+native OpenCV project and failed quickly. Gradle removed some plugin for native code integration, another plugin was no longer maintained, it had internal check for gradle version and it said "I'm designed to work with gradle >= 1.x < 3.x" and just refused to run under 6.x ... I would have to fork that plugin, make it work with newer Gradle or find replacement. I was obviously too lazy and stopped working on that project before I even started.

I'm sure if (would) put more effort into making the build process reproducible, it would work effortlessly, but I didn't care at the point. I wrote it using beta release of OpenCV that's also no longer maintained, because there are better, faster official alternatives available.