I heard of a thing called Hotswap debugging, but I haven't figured out how to use it.

I can't find a download anywhere, nor can I find a thing called hotswap debugging in the debug menu (I use Eclipse).

Just wondering,

Hotswap just refers to automatically applying changes to your current debug session without need to stop, compile and restart the session. From some quick reading, Eclipse is supposed to do this for you automatically if you save changes that you make while debugging a file. You'll need to be sure that 'Build automatically' is enabled in your project.

Hotswap does have some limits like not being able to make schema changes such as adding/removing properties or methods, etc.