Hey, we don't let you delete Main.java because Repl.it is all about having sensible defaults, loading really quick, and not being overly fussy and configurable and allow for everything under the sun.

However, we do have some configuration hooks -- the run command is bound to an entrypoint (in this case Main.java). If you want to configure it, you can do so: https://docs.repl.it/repls/dot-replit

Finally, we're a bit conservative with language versions but will probably upgrade Java soon :)