JTreeの選択されたノードの前後に新規ノードを挿入する

Action addAboveAction = new AbstractAction("insert preceding sibling node") {
  @Override public void actionPerformed(ActionEvent e) {
    JTree tree = (JTree) getInvoker();
    DefaultTreeModel model = (DefaultTreeModel) tree.getModel();
    MutableTreeNode self = (MutableTreeNode) path.getLastPathComponent();
    MutableTreeNode parent = (MutableTreeNode) self.getParent();
    MutableTreeNode child = new DefaultMutableTreeNode("preceding sibling");
    int index = model.getIndexOfChild(parent, self);
    parent.insert(child, index);
    model.reload(parent);
    // or: model.insertNodeInto(child, parent, index);
  }
};
Action addBelowAction = new AbstractAction("insert following sibling node") {
  @Override public void actionPerformed(ActionEvent e) {
    JTree tree = (JTree) getInvoker();
    DefaultTreeModel model = (DefaultTreeModel) tree.getModel();
    MutableTreeNode self = (MutableTreeNode) path.getLastPathComponent();
    MutableTreeNode parent = (MutableTreeNode) self.getParent();
    MutableTreeNode child = new DefaultMutableTreeNode("following sibling");
    int index = model.getIndexOfChild(parent, self);
    parent.insert(child, index + 1);
    model.reload(parent);
    // or: model.insertNodeInto(child, parent, index + 1);
  }
};