@Override
    public String toString() {
        String txt = "";
        if (label != null && !label.equals("")) {
            txt += label + ": \n";
        }
        if (vertices != null && vertices.size() > 0) {
            txt = txt + "V: {";
            for (Vertex v : vertices) {
                txt = txt + v.getLabel() + ", ";
            }
            txt = txt.substring(0, txt.length() - 2) + "}";
        }
        if (edges != null && edges.size() > 0) {
            txt += "\nE: {";
            for (Edge e : edges) {
                txt = txt + e + ", ";
            }
            txt = txt.substring(0, txt.length() - 2) + "}";
        }
        return txt;
    }