Plane Ticket if I got X1 visa for China.

A few days ago I got my X1 with the intention to study for one year in Chengdu.
My question is about plane ticket, do I have to buy a one way ticket? or do I have to buy round trip? Because my intention is not to go back to Japan(Yes. I'm in japan now). After completing one year of study, I have intended to travel back to my home country or continue studying.
I would appreciate your response, thank you very much.