// Fragment - Search for an item in Binary Search Tree

T retrieveItem(TreeNode<T extends KeyedItem> n, long searchKey)
  // returns a node containing the item with the key searchKey
  // or null if not found
  {
    if (n == null) {
      return null;
    }
    else {
      if (searchKey == n.getItem().getKey()) {
        // item is in the root of some subtree
        return n.getItem();
      }
      else if (searchKey < n.getItem().getKey()) {
        // search the left subtree
        return retrieveItem(n.getLeft(), searchKey);
      }
      else { // search the right subtree
        return retrieveItem(n.getRight(), searchKey);
      }  // end if
    }  // end if
  }  // end retrieveItem