code: public void setItemIds(@Nullable ItemIds<? super T> itemIds) {
          if (this.itemIds != itemIds) {
              this.itemIds = itemIds;
              setHasStableIds(itemIds != null);
          }
      }
docs: Set the item id's for the items. If not null, this will set {@link
  RecyclerView.Adapter#setHasStableIds(boolean)} to true.