Sorting a list of triples within a map using one of the values of the triple

Question

I have a hashmap with a triplet like this:

HashMap<String, List<Triplet<String,Integer,Integer>>> output = new HashMap<String, List<Triplet<String,Integer,Integer>>>();

Where the key is a file name and triplet contains information of a word and its frequency information(tf and df).Eg

{File1 = {coffee,23,1},{caffeine,12,2},{brew,9,1}; File2 = {}.......}

I want to sort the values of this list of triples according to the second value of the triplet ie tf (term frequency).

for (Entry<String, List<Triplet<String, Integer, Integer>>> entry : output.entrySet()) {
    String key = entry.getKey();
    List<Triplet<String, Integer, Integer>> value = entry.getValue();

What will come next?

Here's what Triplet looks like:

public class Triplet<T, U, V> {

    private final T first;
    private final U second;
    private final V third;

    public Triplet(T first, U second, V third) {
        this.first = first;
        this.second = second;
        this.third = third;
    }

    public T getFirst() { 
        return first;
    }

    public U getSecond() { 
        return second; 
    }

    public V getThird() {
        return third; 
    }
}

Any help, guidance will be appreciated.

Answer 1

There are 2 ways than came into my mind:

1. make your Triplet Comparable

2. write a Comparator

Than you can either sort the List or use eg a TreeSet

Answer 2

If you can not change your Triplet class by implementing Comparable on it, this would be a solution, using the Collections.sort method:

for (Entry<String, List<Triplet<String, Integer, Integer>>> entry : output.entrySet()) {
        String key = entry.getKey();
        List<Triplet<String, Integer, Integer>> value = entry.getValue();

        // This sorts the list using the anonymous instantiated Comparator class
        Collections.sort(value, new Comparator<Triplet<String, Integer, Integer>>(){
            @Override
            public int compare(Triplet<String, Integer, Integer> object1, Triplet<String, Integer, Integer> object2) {
                return object1.getSecond().compareTo(object2.getSecond());
            }
        });

Or, in a more generic way, without using hard types:

Collections.sort(value, new Comparator<Triplet>(){
                @Override
                public int compare(Triplet object1, Triplet object2) {
                    return object1.getSecond().compareTo(object2.getSecond());
                }
            });

Answer 3

What about this?

public class Triplet<T, U, V> implements Comparable<Triplet<T, U, V> > {

    private final T first;
    private final U second;
    private final V third;

    public Triplet(T first, U second, V third) {
        this.first = first;
        this.second = second;
        this.third = third;
    }

    public T getFirst() { 
        return first;
        }
    public U getSecond() { 
        return second; 
        }
    public V getThird() {
        return third; 
        }
    public int compareTo(Triplet<T, U, V> comparetrpl) {
        T a = comparetrpl.getFirst();
        //ascending order
        return (this.first > a) ? 1 : 0;

        //descending order
        //return (a > this.first) ? 1 : 0;

    }
}

And the use sort method?