I don't understand the attraction...
If you're doing serious development, you need a desktop. If you're on a tablet (and therefore unable to use a desktop based IDE) you're not doing serious development. You might review something. You might even do a couple of lines of code to fix something, but you can do that through your cloud-based git repository UI without the need for a browser-based IDE. I simply don't understand the browser-based IDE concept. Unless, I guess, you have a Chromebook. But again, that isn't a serious developer's piece of kit.
As to developing Java - just use the best IDE (IDEA) and be done with it.
Hmmmm. Maybe I'm a fossil, but this seems to be a solution looking for a problem.