Would the RK3399 fit too? It's a bit faster and already used in the pinebook pro and pinephone pro, so there is a big community around. Apparently there is a more efficient RK3399S version specifically for the pinephone, but I'm not sure it can be sourced.
Also, someone would have to put a huge effort in to make it work, just so you can run a few lines of java code on it. Why not program in C in the first place?