Sometimes, when you're making changes to your code, you want to immediately see how they will behave in a working application without shutting down the process. The HotSwap mechanism lets you reload classes changed during a debugging session without having to restart the entire application.

Suspend the program.

Press ⌘ ⇧ K and start typing Reload Changed Classes. Select the Reload Changed Classes action.

Due to VM design, HotSwap has the following limitations:

it is only available if a method body is modified. Changing signatures is not supported.

adding and removing class members is not supported

if the modified method is already in the call stack, the changes will take effect only after the program exits the modified method. Until that moment, the method body remains unchanged, and the frame is marked as obsolete.

If you want to remove the limitations imposed by the standard VM, you can use the Dynamic Code Evolution VM with unlimited support for reloading classes at runtime.