import javax.swing.tree.*;

static <A> JTree jDynamicTree(final A root, final F1<A, L<A>> makeChildren, fO... optParams) {
  ret swing(func -> JTree {
    DefaultMutableTreeNode rootNode = new(root);
    rootNode.add(new DefaultMutableTreeNode(jDynamicTree_dummy()));
    final JTree tree = new JTree(rootNode);
    tree.setShowsRootHandles(true);
    tree.collapseRow(0);
    final bool keepChildrenOnCollapse = optParam(optParams, 'keepChildrenOnCollapse, false);
    
    tree.addTreeWillExpandListener(new TreeWillExpandListener {
      public void treeWillCollapse(TreeExpansionEvent e) {}
      public void treeWillExpand(TreeExpansionEvent e) pcall {
        DefaultMutableTreeNode node = cast e.getPath().getLastPathComponent();
        if (!keepChildrenOnCollapse || jDynamicTree_isInDummyState(node)) {
          L<A> l = callF(makeChildren, (A) node.getUserObject());
          if (replaceTreeNodeChildren_withDummyChild(node, l, jDynamicTree_dummy()))
            ((DefaultTreeModel) tree.getModel()).nodeStructureChanged(node);
        }
      }
    });
    
    ret tree;
  });
}