How to sort a treemap based on its values?

Question

How can I sort a treemap using its values rather than the key?

Answer 1

Try below code it works fine for me. You can choose both ascending as well as descending order for sorting.

package com.rais;

import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;

public class SortMapByValue
{
    public static boolean ASC = true;
    public static boolean DESC = false;

    public static void main(String[] args)
    {

        // Creating dummy unsorted map
        Map unsortMap = new HashMap();
        unsortMap.put("B", 55);
        unsortMap.put("A", 80);
        unsortMap.put("D", 20);
        unsortMap.put("C", 70);

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

        System.out.println("After sorting ascending order......");
        Map sortedMapAsc = sortByComparator(unsortMap, ASC);
        printMap(sortedMapAsc);


        System.out.println("After sorting descindeng order......");
        Map sortedMapDesc = sortByComparator(unsortMap, DESC);
        printMap(sortedMapDesc);

    }

    private static Map sortByComparator(Map unsortMap, final boolean order)
    {

        List> list = new LinkedList>(unsortMap.entrySet());

        // Sorting the list based on values
        Collections.sort(list, new Comparator>()
        {
            public int compare(Entry o1,
                    Entry o2)
            {
                if (order)
                {
                    return o1.getValue().compareTo(o2.getValue());
                }
                else
                {
                    return o2.getValue().compareTo(o1.getValue());

                }
            }
        });

        // Maintaining insertion order with the help of LinkedList
        Map sortedMap = new LinkedHashMap();
        for (Entry entry : list)
        {
            sortedMap.put(entry.getKey(), entry.getValue());
        }

        return sortedMap;
    }

    public static void printMap(Map map)
    {
        for (Entry entry : map.entrySet())
        {
            System.out.println("Key : " + entry.getKey() + " Value : "+ entry.getValue());
        }
    }
}