code: public int getPosition(Item item) {
          if (item.getIdentifier() == -1) {
              Log.e("FastAdapter", "You have to define an identifier for your item to retrieve the position via this method");
              return -1;
          }
          return getPosition(item.getIdentifier());
      }
docs: Searches for the given item and calculates its global position
  
  @param item the item which is searched for
  @return the global position, or -1 if not found