I currently live in a dormitory in Japan, and all the occupants are non muslim except me. There is a microwave in the pantry that can be used for all occupants. Is it permissible for me to use it? Because the probability of them using the microwave to heat up non halal food such as pork, non halal beef is high (even though im not 100% sure) and I am afraid my food will be contaminated.

Yes it’s permissible for you to use this microwave and the Law of Purity applies.