Do I need a return ticket?

Hi! I've been accepted to study in Hong Kong as an exchange student for the fall semester. I'll be traveling there in late August and leaving sometime in December. I am from Finland and have already applied for student visa. I'm not aware of the exact date when I'll be leaving from HK but do I still need to buy a return ticket? Or is it possible to travel to there with a one way ticket? Thank you in advance! :)