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


this question has answer here:

i trying sort bunch of numbers , have 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, above exception. please help. thanks.

you're comparator doesn't return 0 if both objects equal.

see post: comparison method violates general contract in java 7


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