Clojure has excellent support for hot swapping functions and data; which in my experience is far ahead of anything that Java has. The system introduced in this article is for reloading code but with a consistent state.

For example, if your application includes some state from previous actions. Then you change a function that acts on that state, but with a different protocol (e.g. data structure expectations changed in the function). Then your application would not work, as the old state is invalid for the new function. With techniques like explained in the article, you can quickly "reboot" your state to be consistent with your new code by reseeding your system.