Java - Sort a TreeMap by Values with Comparator

The collection TreeMap is by default sorted by its keys, but if you need to sort TreeMap by values then Java provides a way to do this using the comparator.

Example:

package codeurjava; 

import java.util.*; 

class TreeMapSort {
 
 // Sort TreeMap elements by values
 public static > Map sortByValues(final Map map) {
 
 Comparator valueComparator = new Comparator() {
 public int compare(K k1, K k2) {
 int compare = map.get(k1).compareTo(map.get(k2)); 
 if (compare == 0) 
 return 1; 
 else 
 return compare; 
 }
 }; 
 
 Map TreeMap_triee_par_valeur = new TreeMap(valueComparator); 
 TreeMap_triee_par_valeur.putAll(map); 
 return TreeMap_triee_par_valeur; 
 }
 
 public static void main(String args[]) {
 
 TreeMap treemap = new TreeMap(); 

 // elements
 treemap.put("1", "e4"); 
 treemap.put("2", "e5"); 
 treemap.put("3", "e1"); 
 treemap.put("4", "e3"); 
 treemap.put("5", "e2"); 
 
 System.out.println("Before sorting:"); 
 
 /* browse the unsorted TreeMap with Iterator */
 
 Set set = treemap.entrySet(); 
 Iterator i = set.iterator(); 
 // Show elements
 while(i.hasNext()) {
 Map.Entry entry = (Map.Entry)i.next(); 
 System.out.print(entry.getKey() + " : "); 
 System.out.println(entry.getValue()); 
 }
 
 System.out.println("After sorting:"); 
 // call the sortByvalues()
 Map method TreeMap_triee_par_valeur = sortByValues(treemap); 
 
 /* browse the new map sorted with Iterator */
 
 set = TreeMap_triee_par_valeur.entrySet(); 
 i = set.iterator(); 
 // Show elements
 while(i.hasNext()) {
 Map.Entry entry = (Map.Entry)i.next(); 
 System.out.print(entry.getKey() + " : "); 
 System.out.println(entry.getValue()); 
 }
 
 }
}

Execution

Before sorting: 
1 : e4
2 : e5
3 : e1
4 : e3
5 : e2
After sorting:
3 : e1
5 : e2
4 : e3
1 : e4
2 : e5

References:

Java Documentation - Comparator (JavaSE 8)