@Override
public int compare(Passage o1, Passage o2) {
String qid1 = o1.getQuestion().getId();
String qid2 = o2.getQuestion().getId();
int tmp = qid1.compareTo(qid2);
if (tmp != 0) return tmp; // question id in ascending order
Double score1 = o1.getScore();
Double score2 = o2.getScore();
return score2.compareTo(score1); // score in descending order
}