The Whole Q&A object is child class that parent product (or itemID) class uses.
I believe ArrayList<Items> items; does not belong in this class, but instead it belongs to its parent class for items , which uses this Q&A class. This class keeps a data member for itemID, and will be stored in implicit object first time this classes object is instantiated with appropriate constructor.
Also, all the post Questions and Post Answer function does not need item Id, as it is implied for the same object, once that object contextualized.
(For this Q&A object can and does belong to one unique product ItemId.)