Java error: Comparison method violates its general contract

Question

I saw many questions about this, and tried to solve the problem, but after one hour of googling and a lots of trial & error, I still can\'t fix it. I hope some of you ca

Answer 1

        if (card1.getRarity() < card2.getRarity()) {
            return 1;

However, if card2.getRarity() is less than card1.getRarity() you might not return -1.

You similarly miss other cases. I would do this, you can change around depending on your intent:

public int compareTo(Object o) {    
    if(this == o){
        return 0;
    }

    CollectionItem item = (CollectionItem) o;

    Card card1 = CardCache.getInstance().getCard(cardId);
    Card card2 = CardCache.getInstance().getCard(item.getCardId());
    int comp=card1.getSet() - card2.getSet();
    if (comp!=0){
        return comp;
    }
    comp=card1.getRarity() - card2.getRarity();
    if (comp!=0){
        return comp;
    }
    comp=card1.getSet() - card2.getSet();
    if (comp!=0){
        return comp;
    }   
    comp=card1.getId() - card2.getId();
    if (comp!=0){
        return comp;
    }   
    comp=card1.getCardType() - card2.getCardType();

    return comp;

    }
}