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Saturday, April 22, 2023

How to use TreeSet in Java? SortedSet Example Tutorial

Hello friends, we meet again for our journey of learning Java. Today, we are gonna learn something very fruitful and easy. Hope you all are excited and ready. I would recommend you guys to go through the HashSet article which goes over hashing and what sets are actually as this topic has some of its features. So, What's the wait? Let's start! Continuing our example used in HashSet and reusing it here. Suppose you guys are given the task of storing car names (yes, I love cars :p). Now, how would you store it? This question has already been answered by our HashSet article. The new problem here is, we need to store the names in a naturally sorted manner. As we have a set of String, we need to sort them alphabetically. How to do that?

Think for a few minutes and keep in mind something about hashing and HashSet :p

Now, you guys must be thinking of what we did in TreeMap and using TreeMap here. But, the same problem as the similar idea in HashSet posed is posed here. what to store in value? 

Do not worry. we will go through this problem in our article and let Java handle that value part and use something similar to HashSet but which caters to our needs well.


TreeSet is one of the most prominent Java implementations of the SortedSet interface that stores data in a Tree. Whether or not an explicit comparator is supplied, a set maintains the order of the items by utilizing their natural ordering. If the Set interface is to be effectively implemented, this must be compatible with equals.

Objects are sorted and stored in ascending order according to their natural order in this approach. A self-balancing binary search tree, more precisely a Red-Black tree, is used by the TreeSet.

Simply said, each node of the binary tree contains an additional bit that is used to determine the color of the node, which is either a red or black because it is a self-balancing binary search tree. These "color" bits assist ensure that the tree stays more or less balanced during future insertions and deletions.

Now that we have seen what a TreeSet is, How do they work internally? Let's see.

Working of TreeSet in Java

TreeSet is essentially a Red-Black Tree implementation of a self-balancing binary search tree. As a result, operations such as adding, removing, and searching require O(log(N)) time. The reason for this is that in a self-balancing tree, the height of the tree is guaranteed to be O(log(N)) for all operations.

As a result, this is regarded as one of the most efficient data structures for storing and processing large amounts of sorted data. Printing N elements in sorted order, on the other hand, takes O(N) time.

How to use TreeSet in Java? Example

A TreeSet's implementation is not synchronized. This means that if multiple threads visit a tree set at the same time and at least one of them alters it, the set must be externally synchronized. This is usually achieved by synchronizing some object that wraps the set naturally. 

If no such object exists, use the Collections.synchronizedSortedSet method to encapsulate the set. To avoid unintended unsynchronized access to the set, this should be done at the time of creation.

Now, let's see the working code using our previous article, HashSet's example.


import java.util.Set;
import java.util.TreeSet;

public class MyHashSet {
public static void main(String[] args) {
Set<String> myCarSet = new TreeSet<>();

myCarSet.add("BMW M3");
myCarSet.add("Audi A8");
myCarSet.add("Mercedes Q3");
myCarSet.add("Bugatti veyron");
myCarSet.add("Ferrari spider");

myCarSet.forEach(a -> System.out.print(a+" "));

System.out.println("Traversal completed!");

if(myCarSet.contains("BMW M3")) System.out.println("Yes! BMW hai");

myCarSet.remove("BMW M3");

System.out.println("Traversal started!");

myCarSet.forEach(a -> System.out.print(a + " "));

System.out.println("Traversal completed!");


As you all can see, the output is in sorted way. 

Now, let us see some important points of TreeSet and some advantages and disadvantages.

Important points:

  • Like HashSet, the Java TreeSet class only has unique items. 
  • The access and retrieval speeds for the Java TreeSet class are quite quick. 
  • Null elements are not allowed in the Java TreeSet class. 
  • The TreeSet class in Java isn't synchronized. 
  • The TreeSet class in Java keeps ascending/natural order.

I know you guys are now comfortable with TreeSet. but, I will list down 1-2 questions and it's answers which can be useful for you all.

What is Natural Ordering in TreeSet Java?

  • The ordering suggested by the implementation of the Comparable interface by the objects in the TreeSet is known as "natural" ordering. RBTree must be able to determine which item is smaller than another, and there are two approaches to provide this logic to the RB Tree implementation:
  • In the class(es) used as TreeSet objects, we must implement the Comparable interface.
  • Provide an implementation of the Comparator that performs comparisons outside of the class.

Why do we need TreeSet when we already had SortedSet in Java?

  • TreeSet is the class that implements the sortedSet interface. We all know that we can't construct interface objects in Java. The concrete class that implements the interface must meet the interface's contract, which means it must implement all of the interface's methods. One such implementation is TreeSet.

This is what TreeSet is used for. It is similar to HashSet, but keeps the elements in sorted manner. The sorting is done on the basis on natural ordering by default. You can also provide a comparator explicitly in the constructor so that the sorting can be done on that basis.

Other Java Collection  tutorials  you may like
  • How does get() method of HashMap work in Java? (answer)
  • What is the difference between HashSet and HashMap in Java? (answer)
  • Difference between ConcurrentHashMap and HashMap in Java? (answer)
  • How HashSet internally works in Java? (answer)
  • How ConcurrentHashMap internally works in Java? (answer)
  • The difference between HashMap and LinkedHashMap in Java? (answer)
  • The best way to iterate over HashMap in Java? (answer)
  • Difference between HashMap and Hashtable in Java? (answer)
  • What is the difference between ArrayList and HashMap in Java? (answer)
  • How to sort the HashMap on keys and values in Java? (solution)
  • 3 ways to loop over a Map in Java? (example)
  • The difference between HashMap and ConcurrentHashMap in Java? (answer)
  • What is the difference between ArrayList and HashMap? (difference)
  • How to convert Map to List in Java? (solution)

Thanks for reading this article so far. If you like this TreeSet in Java article then please share with your friends and colleagues. If you have any questions or feedback, please ask in comments. 

P. S. - If you are new to Java and want to learn core Java in depth, you can also checkout these 10 Free Core Java Courses to start with. It contains best free Java courses from Udemy and Coursera for beginners. 

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