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

Question

Why does this code

public class SponsoredComparator implements Comparator {

    public boolean equals(SRE arg0, SRE arg1){
        return arg0.g         


        

Answer 1

I suspect the problem occurs when neither value is sponsored. That will return 1 whichever way you call it, i.e.

x1.compare(x2) == 1

x2.compare(x1) == 1

That's invalid.

I suggest you change this:

object1.getSponsored() && object2.getSponsored()

to

object1.getSponsored() == object2.getSponsored()

in both places. I would probably actually extract this out a method with this signature somewhere:

public static int compare(boolean x, boolean y)

and then call it like this:

public int compare(SRE object1, SRE object2) {
    return BooleanHelper.compare(object1.getSponsored(), object2.getSponsored());
}

That will make the code clearer, IMO.