Java program to convert HashMap to TreeMap

In this article, we will convert a HashMap to a TreeMap in Java. A HashMap is used for storing data as key-value pairs, but it doesn?t keep the keys in any particular order. A TreeMap sorts the keys in ascending order. By converting a HashMap to a TreeMap, we can ensure that the keys are stored in a sorted way.

Problem Statement

Given a HashMap filled with key-value pairs, we need to convert it into a TreeMap so that the entries are sorted by the keys.
Input

("1", "A"), ("2", "B"), ("3", "C"), ("4", "D"), ("5", "E"), <br>("6", "F"), ("7", "G"), ("8", "H"), ("9", "I")<br>

Output

Sorted Map = {1=A, 2=B, 3=C, 4=D, 5=E, 6=F, 7=G, 8=H, 9=I}

Steps to convert HashMap to TreeMap

The following are the steps to convert HashMap to TreeMap ?

• Import the HashMap, TreeMap, and Map classes from the java.util package.
  
• Create a HashMap and fill it with some key-value pairs.
  
• Use the constructor of TreeMap, passing the HashMap as an argument, to automatically sort the keys.
  
• Return the TreeMap to see the keys sorted in ascending order.

Java program to convert HashMap to TreeMap

The following is an example of converting HashMap to TreeMap ?

import java.util.HashMap;
import java.util.Map;
import java.util.TreeMap;
public class Demo {
	public static void main(String[] a) {
		Map<String, String>map = new HashMap<String, String>();
		map.put("1", "A");
		map.put("2", "B");
		map.put("3", "C");
		map.put("4", "D");
		map.put("5", "E");
		map.put("6", "F");
		map.put("7", "G");
		map.put("8", "H");
		map.put("9", "I");
		Map<String, String>sorted = new TreeMap<String, String>(map);
		System.out.println("Sorted Map = "+sorted);
	}
}

Output

Sorted Map = {1=A, 2=B, 3=C, 4=D, 5=E, 6=F, 7=G, 8=H, 9=I}

Code Explanation

Create a HashMap and add some key-value pairs. After that, we use the TreeMap constructor to automatically sort the entries based on the keys. The result is a TreeMap, where the keys are sorted in ascending order, and we return the final output.