How to create a lazy loading JTree

Question

    tree.addTreeExpansionListener(new TreeExpansionListener() {
        @Override
        public void treeExpanded(TreeExpansionEvent event) {
            DefaultMutableTreeNode node = (DefaultMutableTreeNode) event
                            .getPath().getLastPathComponent();
            node.removeAllChildren();
            //System.out.println(node.getChildCount());
            child = new DefaultMutableTreeNode("new node");
            node.add(child);;

            frame.doLayout();
            frame.repaint();

        }

        @Override
        public void treeCollapsed(TreeExpansionEvent event) {
            // TODO Auto-generated method stub

        }
    });