HashSet to TreeSet conversion in Java

Hello guys, today we are about to learn how to convert HashSet to TreeSet in Java. Firstly I want to give a piece of short information related to HashSet and TreeSet.

HashSet and TreeSet class is a member of Collection frameworks. A hash table that stores data value by the means of hashing. Also, it implements set type interface. Positively it stores unique elements.

The following are key points for HashSet –

  • It never contains duplicate elements.
  • It may allow null value too.
  • It’s an unordered collection that doesn’t maintain the order in which they are feed.
  • It uses a HashMap to store all its elements.
  • However, it is not thread-safe.

Tree set

However TreeSet class also implements the set type interface of Collection which helps to use a tree for storage purposes. The speed to access and retrieve elements is fast. The following are important points for TreeSet.

  • It always follows the ascending order.
  • It is not synchronized however it can be possible if it is synchronized explicitly as shown below:

SortedSet sorted_set = Collections.synchronizedSortedSet(new TressSet(…..));

  • It never allows null elements.
  • It also contains a unique element too.


  1. Start
  2. Firstly, take input for operations as a string.
  3. Now, create the HashSet with the appropriate type.
  4. Add all the elements to HashSet by taking user input.
  5. Finally, create a TreeSet of HashSet elements and assign it too.
  6. Show the elements of TreeSet and HashSet.
  7. End


import java.util.*;
public class HashSet_TreeSet {
    public static void main(String args[]){
        Scanner in = new Scanner(System.in);
        System.out.println("Enter number of operations");
        int n = in.nextInt();
        HashSet<String> hashset = new HashSet<String>();
        System.out.println("Enter all the elements");
        for(int i=0;i<n;i++){
        System.out.println("HashSet "+hashset);   
        Set<String> treeset = new TreeSet<String>(hashset);
        System.out.print("TreeSet : ");
        for(String s : treeset)
            System.out.print(s+" ");


Enter number of operations
Enter all the elements
Priya Niharika Jasmine Priyanka Aakriti
HashSet [Priya, Aakriti, Jasmine, Priyanka, Niharika]
TreeSet : Aakriti Jasmine Niharika Priya Priyanka

Also read: Maximum distance between two occurrences of same element in array in Java

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