Sorting on List using Comparator in Java

Question

I have two class

public class PopularSports {    
    public int Rank;    
    public String Sport;
}

public class Medals {
    public String Sport    
    public String Medal    
    public int Year    
    public String Game    
    public String Athlete
}

When i try to lead their csv and get the result in List of each class, I want to sort them in following order.

The PopularSports class should sort in the following order:

Rank
Sport

The Medals class should sort in the following order:

Sport
Medal
Year
Game
Athlete

I have created compactor like this

Collections.sort(medalReportList, new Comparator<Medals >() {
  @Override
  public int compare(Medals o1, Medals o2) {
   return getRankOfSportBySportName(o1.getSport()) > getRankOfSportBySportName(o2.getSport())
          ? +1
          : getRankOfSportBySportName(o1.getSport()) < getRankOfSportBySportName(o2.getSport())
          ? -1
          : o1.getAthlete().compareToIgnoreCase(o2.getAthlete());
    }
  });

But it is not making it happen, it sorts on athlete names.

Ok hope you dont have problem in sorting first list?? How do u want to sort second....?? i.e if sport is same then sort according to medal and if medal is same sort according to game etc ...and so on?? is that u want?? — Shoaib Chikate
– Shoaib Chikate, Commented Oct 31, 2013 at 14:01
What does your getRankOfSportBySportName return? Are you sure it works correctly? — Jesper
– Jesper, Commented Oct 31, 2013 at 14:02
@jesper Thanks for it, yes that function was behaving odd as csv reading was taking " as well while reading — 1Mayur
– 1Mayur, Commented Oct 31, 2013 at 16:20

duffymo · Accepted Answer · 2013-10-31 14:28:14Z

You need to nest those checks. I'll write the PopularSports method and leave the other for you.

I'd recommend that you learn that Java coding standards and make those class names singular: PopularSport and Medal. I'll demonstrate below:

public int compareTo(PopularSport other) {
    if (this.rank < other.rank) return -1;
    else if (this.rank > other.rank) return +1;
    else {
        // This is where the nesting happens to break the ties.
        if (this.sport.compareTo(other.sport) < 0) return -1;
        else if (this.sport.compareTo(other.sport) > 0) return +1;
        else return 0;  // You'll have deeper nesting for the other values in Medal.
    }
}

The order you choose determines which ones are checked first. You nest in the else clause to break the ties.

Admit · Accepted Answer · 2013-10-31 14:08:54Z

0

I would simplify you logic a bit.

public int compare(Medals o1, Medals o2) {
  int rankDifference = getRankOfSportBySportName(o1.getSport()) 
                             - getRankOfSportBySportName(o2.getSport());
  return rankDifference != 0 
      ? rankDifference
      : o1.getAthlete().compareToIgnoreCase(o2.getAthlete());
  }

answered Oct 31, 2013 at 14:08

Admit

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Comments

Mateusz Dymczyk · Accepted Answer · 2013-10-31 14:33:20Z

Others already gave you a solution with ternary operator. I, on the other hand, discourage you from using it in complicated situations - it's simply not readable and hard to maintain.

Either go with if/else blocks (which will look pretty bad with so many fields to compare) or, even better, use a third party library. In Guava you can use ComparisionChain like this:

new Comparator<Medals>() {
    @Override
    public int compare(Medals m1, Medals m1) {
        return ComparisonChain.start()
         .compare(m1.getSport(), m2.getSport())
         .compare(m1.getMedal(), m2.getMedal())
         .compare(m1.getYear(), m2.getYear())
         .compare(m1.getGame(), m2.getGame())
         .compare(m1.getAthlete(), m2.getAthlete(), String.CASE_INSENSITIVE_ORDER)
         .result();
    }
}

Isn't that more readable?!

Shoaib Chikate · Accepted Answer · 2013-10-31 14:08:55Z

Sorting first list will no problem to you. If you want to sort as if sportName is same then sort according to medal and if medal name is same then sort according to year then solution is :

Best way:

public void sortAccordingToAboveRequirement(List<Medal> medals){

 Collections.sort(medals,myComparator);

 }


  static Comparator<Medal> myComparator=new Comparator<Medal>() {
    @Override
        public int compare(Medal medal1, Medal medal2) {
        int value=0;
        value=medal1.getSport().compareTo(medal2.getSport());
        if(value!=0) return value;
        value=medal1.getMedal().compareTo(medal2.getMedal());
        if(value!=0) return value;
        value=medal1.getYear().compareTo(medal2.getYear());
        if(value!=0) return value;
        value=medal1.getGame().compareTo(medal2.getGame());
        if(value!=0) return value;
        value=medal1.getAthlete().compareTo(medal2.Athlete());
        return value;
    }
};

Use compareToIgnoreCase() if you wish :)

Hehehe i took it wrong way your question but very poor way of coding and questioning :(

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