Sorting throws java.lang.IllegalArgumentException: Comparison method violates its general contract -
i have method contains 2 comparators sorting items price.
this works fine 90% of time throws exception in title. know why
void sort( collections.sort(masterlist, new comparator<item>() { @override public int compare(item o1, item o2) { try { if (o1.getpricelevel() == 999 && o1.getpricelevel() < o2.getpricelevel()) { return 1; } if (o2.getpricelevel() == 999) { return -1; } return double.compare(o1.getpricelevel(), o2.getpricelevel()); } catch (exception e) { e.printstacktrace(); return 0; } } }); //null pointer happens on line below collections.sort(masterlist, collections.reverseorder(new comparator<item>() { @override public int compare(item o1, item o2) { try { if (o1.getpricelevel() == 999 || o2.getpricelevel() == 999) { return 1; } return double.compare(o1.getpricelevel(), o2.getpricelevel()); } catch (exception e) { e.printstacktrace(); return 0; } } })); } edit: stacktrace
java.lang.illegalargumentexception: comparison method violates general contract! @ java.util.timsort.mergelo(timsort.java:743) @ java.util.timsort.mergeat(timsort.java:479) @ java.util.timsort.mergecollapse(timsort.java:406) @ java.util.timsort.sort(timsort.java:210) @ java.util.timsort.sort(timsort.java:169) @ java.util.arrays.sort(arrays.java:2038) @ java.util.collections.sort(collections.java:1891)
this check in timsort algorithm used java7 - validates comparator method valid ( e.g. symetric- == b && b == )
your equals case invalid (returning 0) - depends on order arguments given if 1 element null. try handle null values explicitly before doing else e.g.:
if(o1 == null || o2 == null) { return 0; }
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