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How to sort a TreeMap by value in java

By Chaitanya Singh | Filed Under: Java Collections

A TreeMap is always sorted based on its keys, however if you want to sort it based on its values then you can build a logic to do this using comparator. Below is a complete code of sorting a TreeMap by values.

import java.util.*;

class TreeMapDemo {
  //Method for sorting the TreeMap based on values
  public static <K, V extends Comparable<V>> Map<K, V> 
    sortByValues(final Map<K, V> map) {
    Comparator<K> valueComparator = 
             new Comparator<K>() {
      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<K, V> sortedByValues = 
      new TreeMap<K, V>(valueComparator);
    sortedByValues.putAll(map);
    return sortedByValues;
  }
  public static void main(String args[]) {
 
    TreeMap<String, String> treemap = new TreeMap<String, String>();

    // Put elements to the map
    treemap.put("Key1", "Jack");
    treemap.put("Key2", "Rick");
    treemap.put("Key3", "Kate");
    treemap.put("Key4", "Tom");
    treemap.put("Key5", "Steve");
 
    // Calling the method sortByvalues
    Map sortedMap = sortByValues(treemap);
 
    // Get a set of the entries on the sorted map
    Set set = sortedMap.entrySet();
 
    // Get an iterator
    Iterator i = set.iterator();
 
    // Display elements
    while(i.hasNext()) {
      Map.Entry me = (Map.Entry)i.next();
      System.out.print(me.getKey() + ": ");
      System.out.println(me.getValue());
    }
  }
}

Output:

Key1: Jack
Key3: Kate
Key2: Rick
Key5: Steve
Key4: Tom

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Comments

  1. Khushboo Agrawal says

    April 8, 2016 at 9:09 AM

    Hi,
    Here in the above example, after sorting the keys with comparator, you have put the values back in a new Tree HashMap , which will by default sort if by keys.
    You should have put them in a LinkedHashMap instead.

    Reply
  2. amishra says

    March 6, 2017 at 4:16 AM

    is this java8?

    Reply

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