Seems like an interesting effort. A developer is building an alternative Java-based backend to Lemmy’s Rust-based one, with the goal of building in a handful of different features. The dev is looking at using this compatibility to migrate their instance over to the new platform, while allowing the community to use their apps of choice.
Once you know a few languages and the principles for how a computer works moving to a new one is easy. Don’t think of it as being a “Java developer”, but a programmer. It’s just a tool.
We did not learn languages at uni, but concepts. You use the same data structures and algorithms.
I think you’d be surprised, try picking up rust for some advent of code challenges. If you know Java Streams and C/C++ lower level programming all that you’re missing is some pattern matching.
I know Java and I am learning C#, I don’t feel like I can just send a few hours and be at the same level as I am with Java. There are a lot of things I do not know or understand yet with C#.
Anyone can quickly learn how to solve some code challenges in a new language.
It’s a completely different story to learn how to write long lived enterprise scale programs that can grow with multiple independent contributors. This takes a lifetime to learn. More people have more experience to do it with Java.