Question

I am having trouble to sort my collection by Collections.sort() using my own Comparator implementation.
The exception thrown is–>”IllegalArgumentException: Comparison method violates its general contract!
In my OrdersBean I have over-ridden the hashCode as this:

@Override    
    public int hashCode() {
    return this.getServiceOrderName().toUpperCase().hashCode();
}

I have not over-ridden equals() and using that of the Object class only(should not be a problem I feel).

And I have implemented the comparator as this:

public static final Comparator<OrdersBean> ordersComparator=new Comparator<OrdersBean>() {

    @Override
    public int compare(OrdersBean first, OrdersBean second)
    {
        if(Double.parseDouble(first.getPriority())<Double.parseDouble(second.getPriority()))
            return -1;
        else
            if(Double.parseDouble(first.getPriority())>Double.parseDouble(second.getPriority()))
                return +1;
            else
            {
                if((first.getPlatformType().equalsIgnoreCase("EV-DO Carrier ADD")) &&
                        (second.getPlatformType().equalsIgnoreCase("EV-DO Carrier ADD")))
                            return -1;

                if((first.getPlatformType().equalsIgnoreCase("T1 Augment")) &&
                        (second.getPlatformType().equalsIgnoreCase("T1 Augment")))
                            return -1;

                if(first.getPlatformType().equalsIgnoreCase("EV-DO Carrier ADD"))
                    return -1;
                else
                    if(second.getPlatformType().equalsIgnoreCase("EV-DO Carrier ADD"))
                        return +1;
                    else
                        if(first.getPlatformType().equalsIgnoreCase("T1 Augment"))
                            return -1;
                        else
                            if(second.getPlatformType().equalsIgnoreCase("T1 Augment"))
                                return +1;
                            else
                                return -1;
            }

    }
};

Please suggest me , where I am going wrong???

I have changed the code now as follows, Its running fine for sort() method but it is now eventually causing an error in a later code where this comparator is passed to the Tree-Set, where duplicates are not allowed, and thus all the cases of similar platform types where the comparator return 0 , those orders are not added to this sortedSet;(as duplicates are not allowed):

public static final Comparator<OrdersBean> ordersComparator=new Comparator<OrdersBean>() {

    @Override
    public int compare(OrdersBean first, OrdersBean second)
    {
        int diffProrties=(int)(Double.parseDouble(first.getPriority())-Double.parseDouble(second.getPriority()));
        if(diffProrties != 0)
            return diffProrties;

        if(first.getPlatformType().equalsIgnoreCase(second.getPlatformType()))
            return 0;

        if(first.getPlatformType().equalsIgnoreCase("EV-DO Carrier ADD"))
            return -1;
        if(second.getPlatformType().equalsIgnoreCase("EV-DO Carrier ADD"))
            return +1;
        if(first.getPlatformType().equalsIgnoreCase("T1 Augment"))
            return -1;
        if(second.getPlatformType().equalsIgnoreCase("T1 Augment"))
            return +1;

        return 0;


    }
};

Answer 1

compare(a,b) must be the same as -compare(b, a) otherwise there is no deterministic way to compare a and b. You have

if((first.getPlatformType().equalsIgnoreCase("EV-DO Carrier ADD")) &&
   (second.getPlatformType().equalsIgnoreCase("EV-DO Carrier ADD")))
       return -1;

This says a < b AND b < a which makes no sense.