Difference between Tree Set and Hash Set in Java

In Java, HashSet and TreeSet both belong to the collection framework. HashSet is the implementation of the Set interface, whereas TreeSet implements a sorted set. TreeSet is backed by TreeMap while HashSet is backed by a HashMap.

Difference Table

The following are the key differences between HashSet and TreeSet :

Sr. No.	Key	Hash Set	Tree Set
1	Implementation	Hash set is implemented using HashTable	The tree set is implemented using a tree structure.
2	Null Object	HashSet allows a null object	The tree set does not allow the null object. It throws the null pointer exception.
3	Methods	Hash set use equals method to compare two objects	Tree set use compare method for comparing two objects.
4	Heterogeneous object	Hash set doesn't now allow a heterogeneous object	Tree set allows a heterogeneous object
5	Ordering	HashSet does not maintain any order	TreeSet maintains an object in sorted order

TreeSet

Syntax

The Following is the syntax of TreeSet :

TreeSet<String> treeset = new TreeSet<String>();

Example

Below is an example of a TreeSet in Java :

import java.util.TreeSet; public class TreeSetExmaple { public static void main(String[] args){ TreeSet<String> treeset = new TreeSet<String>(); treeset.add("Good"); treeset.add("For"); treeset.add("Health"); //Add Duplicate Element treeset.add("Good"); System.out.println("TreeSet : "); for (String temp : treeset) { System.out.println(temp); } } }

Output

TreeSet: For Good Health

Time complexity: O(log n), due to Red-Black Tree operations.
Space complexity: O(n), stores elements in a balanced tree structure.

HashSet

Syntax

The Following is the syntax of HashSet :

HashSet<String> hashSet = new HashSet<String>();

Example

Below is an example of a HashSet in Java :

import java.util.HashSet; public class HashSetExample { public static void main(String[] args){ HashSet<String> hashSet = new HashSet<String>(); hashSet.add("Good"); hashSet.add("For"); hashSet.add("Health"); //Add Duplicate Element hashSet.add("Good"); System.out.println("HashSet: "); for (String temp : hashSet) { System.out.println(temp); } } }

Output

HashSet: Health For Good

Time complexity: O(n), due to hash collisions.
Space complexity: O(n), stores elements in a Hash Table.