code: public static int computeIndexInParent(Object nodeObject)
      {
          if (nodeObject instanceof DefaultMutableTreeNode)
          {
              DefaultMutableTreeNode node = 
                  (DefaultMutableTreeNode)nodeObject;
              TreeNode parent = node.getParent();
              if (parent == null)
              {
                  return -1;
              }
              int childCount = parent.getChildCount();
              for (int i=0; i<childCount; i++)
              {
                  TreeNode child = parent.getChildAt(i);
                  if (child == nodeObject)
                  {
                      return i;
                  }
              }
          }
          return -1;
      }
docs: Computes the index that the given node has in its parent node.
  Returns -1 if the given node does not have a parent, or the
  node is not a DefaultMutableTreeNode.
  
  @param nodeObject The node
  @return The index of the node in its parent