code: public void updateItem (T item)
      {
          if (_items == null) {
              return;
          }
          int idx = _items.indexOf(item);
          if (idx == -1) {
              _items.add(0, item);
          } else {
              _items.set(idx, item);
          }
      }
docs: Updates the specified item if found in the model, prepends it otherwise.