Java - Comparator

Question

I got question on Comparator - I need to sort my ArrayList<Integer> numbersToSort, which keeps numbers- links to competition.participant.get(numbers.get(index)) - so I have a main Object - competition which has a List of participants object. So, my ArrayList<Integer> numbersToSort keeps which numbers of competition.participants should I use. The only way I figured how to sort my ArrayList<Integer> numbersToSort (which I later will feed to my ListView Adapter) is to make another "parallel"List<Participants> where I shall copy participants from main object, competition and store in them their number in ArrayList<Integer> numbersToSort so I can later assemble a new ArrayList<Integer> sortedNumbers from sorted List<Participant> participants. Are you still there ?:)

    public class ParticipantIndexComparator implements Comparator<Integer> {
        final List<Participant> participants;       
        public ParticipantIndexComparator(ArrayList<Integer> numbersToSort) {
            participants=new ArrayList<Participant>();
            for (int i=0;i<numbersToSort.size();i++)
            { participants.add(i,competition.participant.get(numbersToSort.get(i))); participants.get(i).comparator=numbersToSort.get(i);}

        }

        @Override
        public int compare(Integer i1, Integer i2) {
            long l1 = participants.get(i1).kpTime.get(kpSelected); 
//time from selected checkpoint
            long l2 = participants.get(i2).kpTime.get(kpSelected);
            return (long) compare(l1, l2);
        }
    }

well, the problem is the last return (long) compare(l1, l2); - yes, I know it's not right but it's the 30th attempt :) please correct what's wrong

Why cast to long? Have you tried removing the cast? That looks like a recursive call. Try returning (int)(l1-l2) — NormR
– NormR, Commented Nov 23, 2013 at 12:12
Correction. Need to compare the int values passed to the compare() method. return i1 - i2. — NormR
– NormR, Commented Nov 23, 2013 at 12:20

Mikalai Daronin · Accepted Answer · 2013-11-23 12:18:10Z

2

@Override
public int compare(Integer i1, Integer i2) {
    long l1 = participants.get(i1).kpTime.get(kpSelected); 
    long l2 = participants.get(i2).kpTime.get(kpSelected);
    return Long.compare(l1, l2);
}

answered Nov 23, 2013 at 12:18

Mikalai Daronin

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3 Comments

Vlad Alexeev Over a year ago

The method compare(long, long) is undefined for the type Long

Vlad Alexeev Over a year ago

well, I've found that this is for Java 7+ and I'm on Android sdk which is 6, so it's a little different . it's return Long.valueOf(l1).compareTo(Long.valueOf(l2)); - plz fix it and I'll accept answer.. well, your answer is right anyway:) so I'm accepting

Mikalai Daronin Over a year ago

@user2976267 Just copy method to your project: grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/… And, You can use Java7 on Android: tools.android.com/recent/androidstudio032released

Shayan Pourvatan · Accepted Answer · 2013-11-23 12:13:57Z

0

try this:

        public int compare(Integer lhs,
                        Integer rhs) {
                    return lhs - rhs;
                }
            });

answered Nov 23, 2013 at 12:13

Shayan Pourvatan

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