Sort HashMap by keys in java (ascending & descending order)

Leave a Comment / By Yogesh / May 20, 2016

What is HashMap in java?

HashMap is Hash table based implementation of the Map interface.
HashMap provides constant-time performance for the basic operations (get and put).
HashMap based implementation is not thread safe.
HashMap must synchronized externally, If multiple threads access a hashmap concurrently.
Sort the HashMap by keys in ascending & descending order.
- Map<String, String> mapSportsPersonality = new HashMap<>().
Print the sorted map using forEach method (Java 8)

Program – sort HashMap by keys in ascending & descending order

package org.learn.collection.map.hmap;
 
import java.util.HashMap;
import java.util.Map;
import java.util.TreeMap;
 
public class SortElementInArrayList {
 
    public static void main(String[] args) {
        Map<String, String> mapSportsPersonality = new HashMap<>();
        mapSportsPersonality.put("Tennis", "Federer");
        mapSportsPersonality.put("Cricket", "Bradman");
        mapSportsPersonality.put("Basketball", "Jordan");
        mapSportsPersonality.put("Golf", "Woods");
        mapSportsPersonality.put("Boxer", "Ali");
 
        System.out.println("Demo of sort methods: ");
        demoSortMethod(mapSportsPersonality);       
    }   
 
    private static void demoSortMethod(Map<String, String> mapSportsPersonality) {
        // {Tennis=Federer, Cricket=Bradman, Golf=Woods, Basketball=Jordan, Boxer=Ali}
        System.out.println("Orignal HashMap:" + mapSportsPersonality);
         
        System.out.println("\n1. Sort HashMap by ascending keys: " );
        TreeMap<String,String>mapSorted = new TreeMap<>(mapSportsPersonality);
        mapSorted.forEach((key, value) -> {
            System.out.println(key + ", " + value);
        });
         
        System.out.println("\n2. Sort HashMap by descending keys: " );
        mapSorted.descendingMap().forEach((key, value) -> {
            System.out.println( key + ", "  + value);
        });     
    }   
}

Output – Sort HashMap in ascending & descending order

Demo of sort methods: 
Orignal HashMap:{Tennis=Federer, Cricket=Bradman, Golf=Woods, Basketball=Jordan, Boxer=Ali}
 
1. Sort HashMap by ascending keys: 
Basketball, Jordan
Boxer, Ali
Cricket, Bradman
Golf, Woods
Tennis, Federer
 
2. Sort HashMap by descending keys: 
Tennis, Federer
Golf, Woods
Cricket, Bradman
Boxer, Ali
Basketball, Jordan