How to Sort HashMap by Value

In Java, sorting HashMap by values is complicated because there is no direct method available. If we need to sort the HashMap by values, we should create a Comparator. It compares two elements based on the values.

After that get the Set of elements from the Map and convert Set into the List. Use the Collections.sort(List) method to sort the list of elements by values by passing customized comparator. Now create a new LinkedHashMap and copy the sorted elements into that. Since LinkedHashMap guarantees the insertion order of mappings. We get a HashMap whose values are in sorted order.

Java Collections.sort() method

Java collections class provides a method to sort all list implementations such as LinkedList and ArrayList. There are two overloaded sort methods():

• sort(List list): It sorts the elements of the List in ascending order of their natural order.
• sort(List list, Comparator <T>): It sorts the elements of the list according to the order included by the comparator.

Syntax

The method does not return any value. It throws the following exceptions:

ClassCastException: If the list contains elements that are not mutually comparable.

UnsupportedOperationException: If the specified list’s list-iterator does not support the set operation.

The difference between sorting HashMap by Keys and Values is that it can have duplicate values but not duplicate Keys. We cannot use TreeMap to sort values because TreeMap sorts elements by Keys.

Example of sort HashMap by Value

In the following example, we have sorted the map in ascending and descending order.

Output:

Before sorting:   Company Price  Dell32000  HP20000  Lenovo19990  Samsung36546  Apple65000  Asus21478      Sorting values in ascending order:  Company Price  Lenovo19990  HP20000  Asus21478  Dell32000  Samsung36546  MAC Book65000      Sorting values in descending order:  Company Price  MAC Book65000  Samsung36546  Dell32000  Asus21478  HP20000  Lenovo19990