Set Interface: HashSet (Hashing), LinkedHashSet, and TreeSet (Red-Black Tree)

Intermediate14 min read•Updated: 2026-10-22

🎯 Set Interface: HashSet, LinkedHashSet, and TreeSet

Introduction

A Set is a collection that contains no duplicate elements. The 3 standard implementations offer different ordering guarantees:

📊 The Three Set Implementations

Set Class	Order Guarantee	Performance	Underlying Data Structure
`HashSet`	No Order (Unordered / Arbitrary)	O(1) Fastest	Hash Table (backed by HashMap)
`LinkedHashSet`	Insertion Order preserved	O(1) Fast	Hash Table + Doubly-Linked List
`TreeSet`	Natural Sorted Order (Ascending)	O(log N)	Red-Black Tree (TreeMap)

1import java.util.Set;
2import java.util.HashSet;
3import java.util.TreeSet;
4 
5public class SetDemo {
6    public static void main(String[] args) {
7        Set<String> uniqueCities = new HashSet<>();
8        uniqueCities.add("Shikohabad");
9        uniqueCities.add("Firozabad");
10        uniqueCities.add("Shikohabad"); // Duplicate silently rejected!
11 
12        System.out.println("HashSet (Duplicates rejected): " + uniqueCities.size()); // 2
13 
14        Set<Integer> sortedNumbers = new TreeSet<>(Set.of(45, 12, 89, 23, 7));
15        System.out.println("TreeSet (Automatically Sorted): " + sortedNumbers); // [7, 12, 23, 45, 89]
16    }
17}

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Iterators, ListIterators, and ConcurrentModificationException

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List Interface: ArrayList vs LinkedList (Performance & Internal Arrays)	Iterators, ListIterators, and ConcurrentModificationException

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Iterators, ListIterators, and ConcurrentModificationException

Set Interface: HashSet (Hashing), LinkedHashSet, and TreeSet (Red-Black Tree)

Intermediate14 min read•Updated: 2026-10-22

Study Materials

🎯 Set Interface: HashSet, LinkedHashSet, and TreeSet

Introduction

A Set is a collection that contains no duplicate elements. The 3 standard implementations offer different ordering guarantees:

📊 The Three Set Implementations

Set Class	Order Guarantee	Performance	Underlying Data Structure
`HashSet`	No Order (Unordered / Arbitrary)	O(1) Fastest	Hash Table (backed by HashMap)
`LinkedHashSet`	Insertion Order preserved	O(1) Fast	Hash Table + Doubly-Linked List
`TreeSet`	Natural Sorted Order (Ascending)	O(log N)	Red-Black Tree (TreeMap)

1import java.util.Set;
2import java.util.HashSet;
3import java.util.TreeSet;
4 
5public class SetDemo {
6    public static void main(String[] args) {
7        Set<String> uniqueCities = new HashSet<>();
8        uniqueCities.add("Shikohabad");
9        uniqueCities.add("Firozabad");
10        uniqueCities.add("Shikohabad"); // Duplicate silently rejected!
11 
12        System.out.println("HashSet (Duplicates rejected): " + uniqueCities.size()); // 2
13 
14        Set<Integer> sortedNumbers = new TreeSet<>(Set.of(45, 12, 89, 23, 7));
15        System.out.println("TreeSet (Automatically Sorted): " + sortedNumbers); // [7, 12, 23, 45, 89]
16    }
17}

Next Lesson

Iterators, ListIterators, and ConcurrentModificationException

Continue learning with hands-on practice, examples, and exercises in the upcoming topic.

Related Lessons

Previous Lesson	Next Lesson
List Interface: ArrayList vs LinkedList (Performance & Internal Arrays)	Iterators, ListIterators, and ConcurrentModificationException

Practice Quiz

Test your understanding of this lesson with 1 questions. Each question has one correct answer.

Previous Next