"java.lang.IllegalArgumentException: Comparison method violates its general contract!" error for a Collections.sort()

Question

I am trying to sort a bunch of numbers and have the following code:

//sort possible targets based on distance
                Collections.sort(allPossibleTargets, new Comparator<NPD2>() {
                    @Override
                    public int compare(NPD2 o1, NPD2 o2) {
                        if (o1 == null && o2 == null)
                            return 0;
                        if (o1 == null && o2 != null)
                            return 1;
                        if (o1 != null && o2 == null)
                            return -1;
                        return o1.getNpd().getDistance() < o2.getNpd().getDistance() ? -1 : 1;
                    }
                });

However, I get the above exception. Please help. Thanks.

score 0 · Accepted Answer · edited May 23 '17 at 11:43

0

You're Comparator doesn't return 0 if both objects are equal.

See this post: Comparison Method violates its general contract in Java 7

edited May 23 '17 at 11:43

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answered Mar 31 '15 at 21:54

avojak

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Please don't post link-only answers. Try to explain the issue in the answer. – Maroun Apr 18 '15 at 09:03

"java.lang.IllegalArgumentException: Comparison method violates its general contract!" error for a Collections.sort()

1 Answers1