Difference and similarities between HashSet, LinkedHashSet and TreeSet in Java

Last Updated : 23 Jan, 2026

In Java, HashSet, LinkedHashSet, and TreeSet are implementations of the Set interface, which store unique elements only. While all three prevent duplicate entries, they differ in ordering, internal data structure, and performance.

HashSet

HashSet stores unique elements without maintaining any insertion or sorting order. It internally uses a hash table, which makes it very fast for basic operations like add, remove, and search. HashSet allows one null element.

Output

[20, 10, 30]

Explanation: The output order is not predictable because HashSet does not preserve insertion order or sorting. Duplicate value 10 is ignored since sets allow only unique elements.

LinkedHashSet

LinkedHashSet stores unique elements while preserving the order in which they were inserted. It uses a hash table along with a doubly linked list, making it slightly slower than HashSet but useful when order matters. It also allows one null element.

Output

[Java, Python, C++]

Explanation: Elements are printed in the same order in which they were added to the set. This happens because LinkedHashSet maintains insertion order internally.

TreeSet

TreeSet stores unique elements in sorted order, either by natural ordering or by a custom comparator. It internally uses a Red-Black Tree, which results in slower performance compared to HashSet and LinkedHashSet. TreeSet does not allow null elements.

Output

[10, 30, 40]

Explanation: Even though elements are inserted in random order, TreeSet automatically sorts them in ascending order using natural ordering.

Similarities

All implement the Set interface, so no duplicate elements are allowed. Provide common methods: add(), remove(), contains(), size().

Differences Between HashSet, LinkedHashSet, and TreeSet:

Feature	HashSet	LinkedHashSet	TreeSet
Internal Working	Uses HashMap internally	Uses LinkedHashMap internally	Uses TreeMap internally
Order	No insertion order	Maintains insertion order	Elements sorted by Comparator or natural order
Time Complexity	O(1) for insert, remove, retrieve	O(1) (slightly slower due to linked list maintenance)	O(log n) for insert, remove, retrieve
Performance	Fastest	Slightly slower than HashSet	Slower for insertion/removal due to sorting
Comparison	Uses hashCode() and equals()	Uses hashCode() and equals()	Uses compare() and compareTo()
Null Elements	Allows 1 null	Allows 1 null	Not allowed
Use Case	Store unique elements, order not important	Store unique elements, maintain insertion order	Store unique elements in sorted order
Syntax	HashSet<Type> obj = new HashSet<>();	LinkedHashSet<Type> obj = new LinkedHashSet<>();	TreeSet<Type> obj = new TreeSet<>();