public List<SourceItemNode> getSelectedSourceItemNodes() {
    final List<SourceItemNode> nodes = new ArrayList<>();
    for (DefaultMutableTreeNode treeNode : getSelectedTreeNodes()) {
      final Object userObject = treeNode.getUserObject();
      if (userObject instanceof SourceItemNode) {
        nodes.add((SourceItemNode)userObject);
      }
    }
    return nodes;
  }
public List<SourceItemNode> getSelectedSourceItemNodes()