How to sort a Map in Java

A full Java example to demonstrate how to sort a Map (HashMap) based on its values. The overall idea is, convert the Map into List, sort the List and put the sorted list back to a Map.

Map ---> List ---> Sort ---> Map

Map sorting example

 
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
 
public class SortMapExample{
 
   public static void main(String[] args) {
 
 System.out.println("Unsort Map......");
 Map<String,String> unsortMap = new HashMap<String,String>();
 unsortMap.put("1", "1");
 unsortMap.put("2", "A");
 unsortMap.put("3", "2");
 unsortMap.put("4", "B");
 unsortMap.put("5", "C");
 unsortMap.put("6", "c");
 unsortMap.put("7", "b");
 unsortMap.put("8", "a");
 
 Iterator iterator=unsortMap.entrySet().iterator();
 
        for (Map.Entry entry : unsortMap.entrySet()) {
         System.out.println("Key : " + entry.getKey() 
          + " Value : " + entry.getValue());
        }
 
        System.out.println("Sorted Map......");
        Map<String,String> sortedMap =  sortByComparator(unsortMap);
 
        for (Map.Entry entry : sortedMap.entrySet()) {
         System.out.println("Key : " + entry.getKey() 
          + " Value : " + entry.getValue());
        }
   }
 
   private static Map sortByComparator(Map unsortMap) {
 
        List list = new LinkedList(unsortMap.entrySet());
 
        //sort list based on comparator
        Collections.sort(list, new Comparator() {
             public int compare(Object o1, Object o2) {
            return ((Comparable) ((Map.Entry) (o1)).getValue())
            .compareTo(((Map.Entry) (o2)).getValue());
             }
 });
 
        //put sorted list into map again
 Map sortedMap = new LinkedHashMap();
 for (Iterator it = list.iterator(); it.hasNext();) {
      Map.Entry entry = (Map.Entry)it.next();
      sortedMap.put(entry.getKey(), entry.getValue());
 }
 return sortedMap;
   } 
}

Result

Unsort Map......
Key : 3 Value : 2
Key : 2 Value : A
Key : 1 Value : 1
Key : 7 Value : b
Key : 6 Value : c
Key : 5 Value : C
Key : 4 Value : B
Key : 8 Value : a
Sorted Map......
Key : 1 Value : 1
Key : 3 Value : 2
Key : 2 Value : A
Key : 4 Value : B
Key : 5 Value : C
Key : 8 Value : a
Key : 7 Value : b
Key : 6 Value : c