Hadoop source code: Question about MiniYARNcluster and Application Master

Hi,
I am learning insides of Hadoop by following a map reduce job in Eclipse debugger with break points. I am using MiniYARNcluster. Most of sequence goes according to Hadoop books and lessons I have studied before. Except none of the break points are stopping in ApplicationMaster or MRAppMaster java classes. I see that ApplicationMasterLauncher, ApplicationMasterService, ApplicationMasterProtocol (ApplicationMasterProtocolPBServiceImpl) get invoked, but no actual applicationMaster class.
Can someone please answer: Is there other main application master class that I do not know (besides ApplicationMaster and MRAppMaster)? is ApplicationMaster not always invoked as a class? If yes, what are the cases and what class running services (such as sending container allocation requests) in this case?
Thank you very much,
Sasha