The context is I ran into my friend at school.

These are all things people would say. #3 is a little odd - personally I'd probably say "my math class just *got out*", but I think that's an accent/location thing. People 100% say #3, though. These are all good.

They all sound natural to me. The only possible difference is that 1 (sort of), 2, and 4 all work if you left class early, but 3 does not.

2 and 4 seem the most natural, but I would probably say "I just came from math class" or "I just got out of math class" since it's reasonable to infer that it's your math class because you were in it. In a non-school context I'd be more likely to say "I just came from my spin/cooking/salsa class".

I think all are fine and from all answers, “my” should be removed in order to sound more natural. We already know/assume it’s YOUR class. 3 is most unnatural to me though.

1. ‘Finished’ implies finality or completion without future plans for the math class to meet. This would be most appropriate after a final exam, end of the semester, or end of the academic year. 2. ‘Came from’ tells someone your location before you ran into them. It is precise and easily understood. It is not as casual as #4, but certainly not awkward by any means. 3. See #1. Least natural of those listed. 4. This leaves room for interpretation and is less transferable to other situations and contexts. ‘Got out of’ can simply indicate leaving a situation. However, it carries a small risk of implying you were granted freedom / exemption from an expectation or responsibility that you would rather not partake in if given the choice. It would be fine to use between friends and peers. I would avoid it with authority figures as it can imply you did not want to be in math class. It is the most casual of the options listed, and is likely to be used most often in American English.

They all sound natural and all say very slightly things. The only things I will say is that it would be very common to shorten "my math class" to "math class" or even just "math". It would be perfectly fine to say "I just came from Math" (using "Math" as a name for the activity / class). 1 indicates that you finished, but doesn't say that you left the location of the class (though that is probably implied by context). 2 you came from the class, but you aren't actually saying that you attended class (though it may be implied) 3 math class is finished, but you didn't actually say you went to it or that you just came from it (though that may be implied) 4 you left your math class recently, but you didn't say that it was over or that you've moved away from it (though that may be implied)

Generally I would use #4 "I just got out of class" but all of them would make sense in context, perhaps with slightly different uses. > 1.”I just finished my math class.” This could be also used at the end of the school year to say that your class is completed. > 2.”I just came from my math class.” This would make sense if you were saying that you directly went from math class to your current location. So if someone was asking you where you were you could respond that way. > 3.”my math class just finished.” This makes sense but is perhaps a little unnatural.

When I was in school, I’d probably have said something like “I just finished maths” or “I just had maths”. Both refer to the scheduled time for the maths lesson now being over. I find your first example to sound most natural, personally. Like in British English, Australians say maths and not math, as in common in North America