Sorting a Map object by keys

23 Sep 2023

Convert the Map object to a List of Map.Entry objects.
Sort the List using a custom comparator that compares the keys of the Map.Entry objects.
Create a new Map object and populate it with the sorted entries from the List.

Here’s an example implementation in Java:

import java.util.*;

public class SortMapByKeyExample {
    public static void main(String[] args) {
        // Create a Map object
        Map<Integer, String> map = new HashMap<>();
        map.put(5, "Apple");
        map.put(3, "Banana");
        map.put(1, "Orange");
        map.put(4, "Mango");
        map.put(2, "Grape");

        // Convert Map to List of Map.Entry objects
        List<Map.Entry<Integer, String>> entryList = new ArrayList<>(map.entrySet());

        // Sort the List by keys using a custom comparator
        Collections.sort(entryList, new Comparator<Map.Entry<Integer, String>>() {
            @Override
            public int compare(Map.Entry<Integer, String> entry1, Map.Entry<Integer, String> entry2) {
                return entry1.getKey().compareTo(entry2.getKey());
            }
        });

        // Create a new LinkedHashMap to store the sorted entries
        Map<Integer, String> sortedMap = new LinkedHashMap<>();
        for (Map.Entry<Integer, String> entry : entryList) {
            sortedMap.put(entry.getKey(), entry.getValue());
        }

        // Print the sorted Map
        for (Map.Entry<Integer, String> entry : sortedMap.entrySet()) {
            System.out.println(entry.getKey() + ": " + entry.getValue());
        }
    }
}

In this example, we create a Map object with integer keys and string values. We convert the Map to a List of Map.Entry objects and then use Collections.sort() to sort the list based on the keys. Finally, we create a new LinkedHashMap and populate it with the sorted entries. The resulting sortedMap contains the same key-value pairs as the original map, but with the keys sorted in ascending order.

By following these steps, you can easily sort a Map object by keys in various programming languages. This approach gives you control over the order of keys in the sorted Map, regardless of the default order of the Map implementation.