Sorting HashMap by value using a TreeMap and Comparator

Question

Im using the following code to create a hashmap and then sort the values in the hashmap by using a treemap and a comparator. However, the output is rather unexpected. So any th

Answer 1

The Java Doc of TreeMap clearly states that:

A Red-Black tree based NavigableMap implementation. The map is sorted according to the natural ordering of its keys

we should not violate this rule by using TreeMap to sort by values.

However to sort by values, we can do the following:

1. Create a LinkedList of entries of the map
2. using Collection.sort to sort the entries
3. Inserting the sorted entries to a LinkedHashMap: keeps the keys in the order they are inserted, which is currently sorted on natural ordering.

4. Return the LinkedHashMap as the sorted map.

    public static  Map sortByValues(Map map){
       List> entries = new LinkedList>(map.entrySet());
   
       Collections.sort(entries, new Comparator>() {
   
           @Override
           public int compare(Entry o1, Entry o2) {
               return o1.getValue().compareTo(o2.getValue());
           }
       });
   
   
       Map sortedMap = new LinkedHashMap();
   
       for(Map.Entry entry: entries){
           sortedMap.put(entry.getKey(), entry.getValue());
       }
   
       return sortedMap;
   }
   
   }
   

Reference: Sorting Map by value