Thank you for your comments! I'm glad you like it!
It should be a good idea to show if you're playing vs human or AI.
Yes, I'm planning to do that. But I don't want to clutter the interface with labels. Maybe the AI-controlled balls should just be drawn differently, e.g. non-shiny. But as you say, it's easy to spot because of its "strategy": Currently it just throws the dice whether it should shoot in the general direction of the sphere or just somwhere random.
No idea if the networking works
It does! You can't play the game with the client alone, otherwise:
It got stuck on "Connecting..."
There seems to be a strange error that only occurs after several hours: The JVM doesn't print any error message but the server doesn't react any more, neither to clients nor to the keyboard. Unfortunately I couldn't reproduce that locally so far.