Swing/PreventNodeExpanding のバックアップ(No.10)

class DirectoryExpandVetoListener implements TreeWillExpandListener {
  @Override public void treeWillExpand(TreeExpansionEvent e)
        throws ExpandVetoException {
    TreePath path = e.getPath();
    Object o = path.getLastPathComponent();
    if (o instanceof DefaultMutableTreeNode) {
      DefaultMutableTreeNode node = (DefaultMutableTreeNode) o;
      File file = (File) node.getUserObject();
      String title = file.getName();
      System.out.println(title);
      if (title.startsWith(".")) {
        throw new ExpandVetoException(e, "Tree expansion cancelled");
      }
    }
  }
  @Override public void treeWillCollapse(TreeExpansionEvent e)
        throws ExpandVetoException {
    // 何もしない(例外を返さない)ので、折り畳みは可能
  }
}