Concordance.java

import java.util.*;

public class Concordance {
    static class Word{
        String text;
        int count;

        public Word(String text, int count ){
            this.text = text;
            this.count = count;
        }

        @Override
        public String toString() {
            return "[" + text + " -- " +count +"]";
        }
    }

    public static List<Word> calculate(String input, int n){

        List<Word> list = new ArrayList<>();

        if (input==null || input.trim()=="")
            return list;

        String [] words = input.split(" ");

        HashMap<String, Integer> map = new HashMap<>();
        PriorityQueue<Word> pq = new PriorityQueue<>((o1, o2)->(o2.count-o1.count));


        for(int i=0; i<words.length; i++){
            String x = words[i].toLowerCase();
            int count = map.getOrDefault(x, 0);
            map.put(x, count+1);
        }

        for(String key: map.keySet()){
            pq.offer(new Word(key, map.get(key)));
        }

        while(n>0){
            list.add(pq.remove());
            n--;
        }
        return list;
    }

    public static void main(String[] args) {
        String text = "Lorem Ipsum is simply dummy text of the printing and" +
                " typesetting industry. Lorem Ipsum has been the industry's" +
                " standard dummy text ever since the 1500s";
        int n = 2;
        System.out.println(text);
        System.out.println(calculate(text, n));
        System.out.println();
        text = "There are many variations of passages of Lorem" +
                " Ipsum available, but the majority have suffered" +
                " alteration in some form by injected humour, or" +
                " randomised words which don't look even slightly of believable form";
        n = 3;
        System.out.println(text);
        System.out.println(calculate(text, n));
    }

}