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 swapping is limited to updating method bodies only, and trying to add methods and fields to classes would not succeed.
Can anyone explain this with code.
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.
来源：https://stackoverflow.com/questions/13564785/jvm-hot-swapping