// Removes an entry from the tree rooted at a given node.
// rootNode is a reference to the root of a tree.
// entry is the object to be removed.
// oldEntry is an object whose data field is null.
// Returns the root node of the resulting tree; if entry matches
//         an entry in the tree, oldEntry's data field is the entry
//         that was removed from the tree; otherwise it is null.
private BinaryNode<T> removeEntry(BinaryNode<T> rootNode, T entry,
                                  ReturnObject oldEntry)
{
   if (rootNode != null)
   {
      T rootData = rootNode.getData();
      int comparison = entry.compareTo(rootData);

      if (comparison == 0)       // entry == root entry
      {
         oldEntry.set(rootData);
         rootNode = removeFromRoot(rootNode);
      }
      else if (comparison < 0)   // entry < root entry
      {
         BinaryNode<T> leftChild = rootNode.getLeftChild();
         BinaryNode<T> subtreeRoot = removeEntry(leftChild, entry, oldEntry);
         rootNode.setLeftChild(subtreeRoot);
      }
      else                       // entry > root entry
      {
         BinaryNode<T> rightChild = rootNode.getRightChild();
         rootNode.setRightChild(removeEntry(rightChild, entry, oldEntry));
      } // end if
   } // end if

   return rootNode;
} // end removeEntry
// Version 4.0