one of the things about
java is that you don't NEED to know. Java has built in memory management, so you don't need to calculate the size to find an offset.
I guess my question to you would be "Why do you want to know? What do you hope to gain by knowing, or do with the info?"
if it's purely an academic exercise, OK, but if you have some pressing design need, there's probably a better way.
There are only two hard things in computer science: cache invalidation, naming things, and off-by-one errors