Sort HashMap by Values

When it comes to sorting a hash map by keys, it can be easily implemented using TreeMap as TreeMap by default sorts a map using key.

But when it comes to sort a map by values, we’ve to make use of Comparator which sorts map values by itself.

import java.util.ArrayList;

import java.util.Collections;

import java.util.Comparator;

import java.util.HashMap;

import java.util.LinkedHashMap;

import java.util.List;

import java.util.Map.Entry;

import java.util.Set;

public class HashMapSort {

     public static void main(String[] args) {

           HashMap<String,String> hashMap = new HashMap<>();

          

           /*Entering values in an Array*/

           hashMap.put("Paras","Chawla");

           hashMap.put("Sonal","Gupta");

           hashMap.put("Richa", "Pruthi");

           hashMap.put("Usha","Pahwa");

          

           System.out.println("Unsorted HashMap "+ hashMap);

          

           /*Putting Entry<String,String> into set*/

           Set<Entry<String,String>> set= hashMap.entrySet();

           System.out.println("Unsorted Set "+set);

           /*Creating list using Set*/

           List<Entry<String,String>> list = new ArrayList<>(set);

           System.out.println("Unsorted List "+list);

          

           /*Creating Comparator*/

           Comparator<Entry<String,String>> comparator = new Comparator<Entry<String,String>>() {

                @Override

                public int compare(Entry<String, String> o1, Entry<String, String> o2) {

                     return o1.getValue().compareTo(o2.getValue());

                }

           };

          

           /*Passing list and comparator to Collections.sort()*/

           Collections.sort(list, comparator);

          

           /*Got sorted list from sort()*/

           System.out.println("Sorted List"+list);

          

           /*Since HashMap doesn't maintain order,

            * Adding Entry key and Entry value from List in LHM */

           LinkedHashMap<String,String> linkedHashMap = new LinkedHashMap<>();

          

           /*Adding from List into LinkedHashMap*/

           for(Entry<String,String> entry : list)

                linkedHashMap.put(entry.getKey(),entry.getValue());

               

           /*For printing we need to add LinkedHashMap to Set again */

           Set<Entry<String,String>> sortedSet = linkedHashMap.entrySet();

          

           System.out.println("Sorted Map");

           for(Entry<String,String> entry : sortedSet)

           System.out.println("Key->"+ entry.getKey()+"| Value-->"+ entry.getValue());

     }

}

Output

Unsorted HashMap {Richa=Pruthi, Paras=Chawla, Sonal=Gupta, Usha=Pahwa}

Unsorted Set [Richa=Pruthi, Paras=Chawla, Sonal=Gupta, Usha=Pahwa]

Unsorted List [Richa=Pruthi, Paras=Chawla, Sonal=Gupta, Usha=Pahwa]

Sorted List[Paras=Chawla, Sonal=Gupta, Usha=Pahwa, Richa=Pruthi]

Sorted Map

Key->Paras| Value-->Chawla

Key->Sonal| Value-->Gupta

Key->Usha| Value-->Pahwa

Key->Richa| Value-->Pruthi