Adapter class is a helper to RecyclerView. It has three responsibilities: To return how many items should be in RecyclerView, inflate item views from XML and return new ViewHolder instance(object). and populate them with appropriate data(Basically, everything is in this order). So, it has (constructor and) three methods:
Constructor:
public MyAdapter(int numberOfItems, ListItemClickListener onClickListener)where ListItemClickListener is an interface, which has one void methoid defined, onListItemClick.