Develop for JOSM core or plugin?

[Tom H.]

Thank you all for your suggestions, I think I've decided to update the core
instead of making a separate plugin, since hotkeys are simple enough to
implement and may get frequent use from users.

I now wonder can anyone point me to the right direction as to where to
begin to integrate new hotkeys into JOSM, like what are the relevant
files/classes I should modify? And further, is there a tutorial to learn
how to create JOSM builds? Or had there been any relevant threads in the
archive? Sorry for all the questions, I'm just very new. Thanks!