JVM HOT Swapping

Question

What is JVM Hot Swapping?

Many definitions say that this feature allows code to updated on the fly during de-bugging.

And a few restrictions such as hot swap

Answer 1

All it means is that you can make certain changes to your code while in the middle of a debugging session, and have those changes take effect immediately, without having to restart the application.

This can be a very handy feature in some circumstances. However, you're typically restricted in what kinds of code changes can be hotswapped into a running application. The exact nature of the restrictions depends on your toolchain.