What technology / method is used to compile Java on the fly ? [video included]

Question

I was watching Notch code Minicraft for the Ludum Dare competition on this twitch VOD and I wonder : what does he use to make the changes he makes in the code take effect instantly in the running instance of the game ?

Twitch link again (@6hours15minutes40seconds)

Answer 1

Eclipse includes a feature called hot swapping, which is used when you press the debug button to run your application.

While you application is running in that mode, you can make changes to the code, save it, and the new code will be swapped in for the old code (if it does not have any errors).