why does my compare method throw exception -- Comparison method violates its general contract!

user_491739 0
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Why does this code 

public class SponsoredComparator implements Comparator<SRE> {

    public boolean equals(SRE arg0, SRE arg1){
        return arg0.getSponsored()==arg1.getSponsored();
    }

    public int compare(SRE object1, SRE object2) {
        Log.d("SponsoredComparator","object1.getName() == "+ object1.getName());
        Log.d("SponsoredComparator","object1.getSponsored() == "+ object1.getSponsored());
        Log.d("SponsoredComparator","object2.getName() == "+ object2.getName());
        Log.d("SponsoredComparator","object2.getSponsored() == "+ object2.getSponsored());
        Log.d("SponsoredComparator","compare return == "+ (object1.getSponsored() && object2.getSponsored() ? 0 : object1.getSponsored() ? -1 : 1));
        return object1.getSponsored() && object2.getSponsored() ? 0 : object1.getSponsored() ? -1 : 1;
    }
}

throw this exception: ERROR/AndroidRuntime(244): java.lang.IllegalArgumentException: Comparison method violates its general contract!
ERROR/AndroidRuntime(4446): at java.util.TimSort.mergeLo(TimSort.java:743)

The method sre.getSponsored() returns a boolean.

Thanks.

contract comparator android java
7 Answers

I got the same problem today in a web application. Four calls working on the same array tried to sort it at the same time, effectively messing up for each other.

user_7974330

My solution: When I want to sort numbers and an array element is null, I put 0 then the error disappears. It is needed to take care that the sizes of each row in the two-dimensional arrays are the same.

user_103690160
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