Swing/CheckBoxGroupEnabling のバックアップ(No.2)

class CheckBoxStatusUpdateListener implements TreeModelListener {
  private boolean adjusting;

  @Override public void treeNodesChanged(TreeModelEvent e) {
    if (adjusting) {
      return;
    }
    adjusting = true;

    DefaultTreeModel model = (DefaultTreeModel) e.getSource();
    Object[] children = e.getChildren();
    boolean isOnlyOneNodeSelected = Objects.nonNull(children) && children.length == 1;
    Object current = isOnlyOneNodeSelected ? children[0] : model.getRoot();
    if (current instanceof DefaultMutableTreeNode) {
      DefaultMutableTreeNode node = (DefaultMutableTreeNode) current;
      CheckBoxNode c = (CheckBoxNode) node.getUserObject();
      for (Object child : e.getChildren()) {
        updateAllChildrenUserObject((DefaultMutableTreeNode) child, c.selected);
      }
      model.nodeChanged((DefaultMutableTreeNode) e.getTreePath().getLastPathComponent());
    }
    adjusting = false;
  }

  private void updateAllChildrenUserObject(DefaultMutableTreeNode parent, boolean enabled) {
    // Java 9: Collections.list(parent.breadthFirstEnumeration()).stream()
    Collections.list((Enumeration<?>) parent.breadthFirstEnumeration()).stream()
        .filter(DefaultMutableTreeNode.class::isInstance)
        .map(DefaultMutableTreeNode.class::cast)
        .filter(node -> !Objects.equals(parent, node))
        .forEach(node -> {
          CheckBoxNode check = (CheckBoxNode) node.getUserObject();
          node.setUserObject(new CheckBoxNode(check.text, check.selected, enabled));
        });
  }

  @Override public void treeNodesInserted(TreeModelEvent e) {
    /* not needed */
  }

  @Override public void treeNodesRemoved(TreeModelEvent e) {
    /* not needed */
  }

  @Override public void treeStructureChanged(TreeModelEvent e) {
    /* not needed */
  }
}