Java Program to Sort map by keys

In this article, we will understand how to sort map by keys. The Java Map interface, java.util.Map, represents a mapping between a key and a value. More specifically, a Java Map can store pairs of keys and values. Each key is linked to a specific value.

Below is a demonstration of the same −

Suppose our input is −

Input map: {1=Scala, 2=Python, 3=Java}

The desired output would be −

The sorted map with the key:
{1=Scala, 2=Python, 3=Java}

Algorithm

Step 1 - START
Step 2 - Declare namely
Step 3 - Define the values.
Step 4 - Create a Map structure, and add values to it using the ‘put’ method.
Step 5 - Create a TreeMap of strings.
Step 6 - The Map sorts the values based on keys and stores it in TreeMap.
Step 7 - Display this on the console.
Step 8 - Stop

Example 1

Here, we bind all the operations together under the ‘main’ function.

import java.util.HashMap;
import java.util.Map;
import java.util.TreeMap;
public class Demo {
   public static void main(String[] args) {
      System.out.println("The required packages have been imported");
      Map<String, String> input_map = new HashMap<>();
      input_map.put("1", "Scala");
      input_map.put("3", "Java");
      input_map.put("2", "Python");
      System.out.println("The map is defined as: " + input_map);
      TreeMap<String, String> result_map = new TreeMap<>(input_map);
      System.out.println("\nThe sorted map with the key: \n" + result_map);
   }
}

Output

The required packages have been imported
The map is defined as: {1=Scala, 2=Python, 3=Java}

The sorted map with the key:
{1=Scala, 2=Python, 3=Java}

Example 2

Here, we encapsulate the operations into functions exhibiting object oriented programming.

import java.util.HashMap;
import java.util.Map;
import java.util.TreeMap;
public class Demo {
   static void sort( Map<String, String> input_map){
      TreeMap<String, String> result_map = new TreeMap<>(input_map);
      System.out.println("\nThe sorted map with the key: \n" + result_map);
   }
   public static void main(String[] args) {
      System.out.println("The required packages have been imported");
      Map<String, String> input_map = new HashMap<>();
      input_map.put("1", "Scala");
      input_map.put("3", "Java");
      input_map.put("2", "Python");
      System.out.println("The map is defined as: " + input_map);
      sort(input_map);
   }
}

Output

The required packages have been imported
The map is defined as: {1=Scala, 2=Python, 3=Java}

The sorted map with the key:
{1=Scala, 2=Python, 3=Java}