I did not know of a Java port, but this reminds me there is some kind of JavaScript-based environment for DOS that I see linked now and then (think it is bundled with FreeDOS?). Probably this one:

https://github.com/SuperIlu/DOjS

"DOjS is a JavaScript programming environment for systems running MS-DOS, FreeDOS or any DOS based Windows (like 95, 98, ME). It features an integrated editor, graphics & sound output, mouse/keyboard/joystick input and more"

Never tried it.