How to sort a HashMap in Java [duplicate]

Answer 1

http://snipplr.com/view/2789/sorting-map-keys-by-comparing-its-values/

get the keys

List keys = new ArrayList(yourMap.keySet());

Sort them

 Collections.sort(keys)

print them.

In any case, you can't have sorted values in HashMap (according to API This class makes no guarantees as to the order of the map; in particular, it does not guarantee that the order will remain constant over time ].

Though you can push all these values to LinkedHashMap, for later use as well.

Answer 2

If you want to combine a Map for efficient retrieval with a SortedMap, you may use the ConcurrentSkipListMap.

Of course, you need the key to be the value used for sorting.

Answer 3

Sorting HashMap by value in Java:

public class HashMapSortByValue {
    public static void main(String[] args) {

        HashMap<Long,String> unsortMap = new HashMap<Long,String>();
            unsortMap.put(5l,"B");
            unsortMap.put(8l,"A");
            unsortMap.put(2l, "D");
            unsortMap.put(7l,"C" );

            System.out.println("Before sorting......");
            System.out.println(unsortMap);

            HashMap<Long,String> sortedMapAsc = sortByComparator(unsortMap);
            System.out.println("After sorting......");
            System.out.println(sortedMapAsc);

    }

    public static HashMap<Long,String> sortByComparator(
            HashMap<Long,String> unsortMap) {

            List<Map.Entry<Long,String>> list = new LinkedList<Map.Entry<Long,String>>(
                unsortMap.entrySet());

            Collections.sort(list, new Comparator<Map.Entry<Long,String>> () {
                public int compare(Map.Entry<Long,String> o1, Map.Entry<Long,String> o2) {
                    return o1.getValue().compareTo(o2.getValue());
                }
            });

            HashMap<Long,String> sortedMap = new LinkedHashMap<Long,String>();
            for (Entry<Long,String> entry : list) {
              sortedMap.put(entry.getKey(), entry.getValue());
            }
            return sortedMap;
          }

}

Answer 4

Sorting by key:

public static void main(String[] args) {
    Map<String,String> map = new HashMap<>();

    map.put("b", "dd");
    map.put("c", "cc");
    map.put("a", "aa");

    map = new TreeMap<>(map);

    for (String key : map.keySet()) {
        System.out.println(key+"="+map.get(key));
    }
}

Answer 5

I developed a fully tested working solution. Hope it helps

import java.io.BufferedReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.List;
import java.util.StringTokenizer;


public class Main {
    public static void main(String[] args) {
    try {
        BufferedReader in = new BufferedReader(new java.io.InputStreamReader           (System.in));
            String str;

        HashMap<Integer, Business> hm = new HashMap<Integer, Business>();
        Main m = new Main();


        while ((str = in.readLine()) != null) {


            StringTokenizer st = new StringTokenizer(str);
            int id = Integer.parseInt(st.nextToken());    // first integer
            int rating = Integer.parseInt(st.nextToken());    // second 

            Business a = m.new Business(id, rating);


            hm.put(id, a);


            List<Business> ranking = new ArrayList<Business>(hm.values());

            Collections.sort(ranking, new Comparator<Business>() {

                public int compare(Business i1, Business i2) {
                    return i2.getRating() - i1.getRating();
                }
            });

            for (int k=0;k<ranking.size();k++) {
                System.out.println((ranking.get(k).getId() + " " + (ranking.get(k)).getRating()));
            }


        }
        in.close();

    } catch (IOException e) {
        e.printStackTrace();
    }


}
public class Business{

    Integer id;
    Integer rating;

    public Business(int id2, int rating2)
    {
        id=id2;
        rating=rating2;

    }

    public Integer getId()
    {
        return id;
    }
    public Integer getRating()
    {
        return rating;
    }


}
}