private void checkAndOutputStyle() {
String nodeStyle = "circle,draw=black,fill=black";
String edgeStyle = "draw=black";
StyleGroupSet sgs = buffer.getStyleGroups();
for (StyleGroup sg : sgs.groups()) {
String key = String.format("class%02d", classIndex++);
classNames.put(sg.getId(), key);
classes.put(key, getTikzStyle(sg));
}