Repl.it doesn't have a display environment (basically something that your code can read and write pixels to) set up that the client can use. Unfortunately, the terminal is the only thing that replit sends the output from over to the client. Not quite sure of a work around for Java.

Try looking into JFrame.

When I tried it a long time ago(like a few months and I stopped trying to learn Java lol) It worked and I was able to display images. Perhaps that might help.

does not work at all