How to sort a `Map<Key, Value>` by values in Java

The Problem

I don’t know how to sort a Map<Key, Value> by its values in Java.

The Solution

There are two ways to sort a map by its values in Java:

• You can use List<Map.Entry<K, V>> to create a list of its entries, then use Collections.sort() to sort that list based on the values of each entry.
• If you use Java version 8 or later, you can use the Stream API to organize the map entries by value in a LinkedHashMap.

Consider the following map as an example:

Map<String, Integer> map = new HashMap<>();

map.put("Apple", 3);
map.put("Banana", 1);
map.put("Kiwi", 4);
map.put("Cherry", 2);

The Banana entry has the lowest value and would appear first in a sorted list.

Using List<Map.Entry<K, V>> and Collections.sort()

You can convert the map’s entry set into a list and use Collections.sort() to sort it based on the values.

import java.util.*;

public class Main {
    public static void main(String[] args) {
        Map<String, Integer> map = new HashMap<>();
        map.put("Apple", 3);
        map.put("Banana", 1);
        map.put("Kiwi", 4);
        map.put("Cherry", 2);

        List<Map.Entry<String, Integer>> list = new ArrayList<>(map.entrySet());
        list.sort(Map.Entry.comparingByValue());

        for (Map.Entry<String, Integer> entry : list) {
            System.out.println(entry.getKey() + " -> " + entry.getValue());
        }
    }
}

This creates a list from the map entries, uses sort() with Map.Entry.comparingByValue() to sort the list by values, and returns the following output:

Banana -> 1
Cherry -> 2
Apple -> 3
Kiwi -> 4

Using the Stream API (Java 8+)

If you are using Java version 8 or later, you can use the Stream API to sort the map by its values and collect the results into a LinkedHashMap to preserve the order of the sorted entries.

import java.util.*;
import java.util.stream.Collectors;

public class Main {
    public static void main(String[] args) {
        Map<String, Integer> map = new HashMap<>();
        map.put("Apple", 3);
        map.put("Banana", 1);
        map.put("Kiwi", 4);
        map.put("Cherry", 2);

        Map<String, Integer> sortedMap = map.entrySet()
                .stream()
                .sorted(Map.Entry.comparingByValue())
                .collect(Collectors.toMap(
                        Map.Entry::getKey,
                        Map.Entry::getValue,
                        (e1, e2) -> e1,  // Merge function
                        LinkedHashMap::new));

        sortedMap.forEach((key, value) -> System.out.println(key + " -> " + value));
    }
}

Running this outputs:

Banana -> 1
Cherry -> 2
Apple -> 3
Kiwi -> 4