I'm a Systems Reliability and DevOps engineer for Netdata Inc. When not working, I enjoy studying linguistics and history, playing video games, and cooking all kinds of international cuisine.
When I look at his code I'm kinda horrified and at the same time not sure if it makes any sense to teach naming conventions etc. at this point.
Good coding habits are important, it's never too early to start teaching them, especially since it becomes harder to learn the longer you put off learning it.
The important thing here is to explain why it matters. Most people have a much easier time learning stuff if they understand why it's important to learn it. Once you've got that, show him how to set up some kind of linting program to help him check his own code (I don't know of any good linters for Java, but I'm talking something akin to ESLint or flake8 here), and configure it so that it just reports errors/warnings instead of fixing them for him. That way, he'll learn over time to recognize and correct such things himself, and eventually start just writing the code that way to begin with.
For further actions, you may consider blocking this person and/or reporting abuse
We're a place where coders share, stay up-to-date and grow their careers.
Good coding habits are important, it's never too early to start teaching them, especially since it becomes harder to learn the longer you put off learning it.
The important thing here is to explain why it matters. Most people have a much easier time learning stuff if they understand why it's important to learn it. Once you've got that, show him how to set up some kind of linting program to help him check his own code (I don't know of any good linters for Java, but I'm talking something akin to ESLint or flake8 here), and configure it so that it just reports errors/warnings instead of fixing them for him. That way, he'll learn over time to recognize and correct such things himself, and eventually start just writing the code that way to begin with.