Set Interface in Java

Quipoin

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Nov 22, 2025

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The Set interface is a part of the Java Collection Framework and is used to store a collection of unique elements.
Unlike List, a Set does not allow duplicate values and doesn’t maintain insertion order (except specific implementations).

Block Diagram of Set Interface

<<Collection>>
               ▲
               |
         <<Set Interface>>
        /        |         \
       /         |          \
<HashSet> <LinkedHashSet> <TreeSet>

▶ << >> : Interface
▶ < > : Class
▶ ----> : Represents Implementation

Implementation Classes of Set Interface

1 HashSet

Uses HashTable for internal storage.

Does not maintain insertion order.

Provides constant-time performance for add, remove & search.

Best for fast operations where ordering doesn’t matter.

Example

import java.util.HashSet;
public class HashSetExample {
    public static void main(String[] args) {
        HashSet<String> set = new HashSet<>();
        set.add("Java");
        set.add("Python");
        set.add("Java"); // Duplicate ignored
        System.out.println(set);
    }
}

Output
[Java, Python] (Order may vary)

2 LinkedHashSet

Maintains insertion order.

Slightly slower than HashSet due to ordering.

Good when you want uniqueness + order.

Example

import java.util.LinkedHashSet;
public class LinkedHashSetExample {
    public static void main(String[] args) {
        LinkedHashSet<Integer> set = new LinkedHashSet<>();
        set.add(30);
        set.add(10);
        set.add(20);
        System.out.println(set);
    }
}

Output
[30, 10, 20]

3 TreeSet

Stores elements in sorted order (ascending by default).

Implements NavigableSet, supports range-based operations.

Slower than HashSet & LinkedHashSet due to sorting.

Example

import java.util.TreeSet;
public class TreeSetExample {
    public static void main(String[] args) {
        TreeSet<Integer> set = new TreeSet<>();
        set.add(50);
        set.add(10);
        set.add(30);
        System.out.println(set);
    }
}

Output
[10, 30, 50]

Advantages of Set

✔ Stores unique elements
✔ Better performance than List for search operations
✔ Useful for removing duplicates

Limitations

✘ No indexing (cannot access using index)
✘ Order not guaranteed in some implementations

For More Learning:

Interview Practice: https://www.quipoin.com/interview/java/set-interface

Video Tutorial: https://youtu.be/r1J4p8d-MP0?si=svU6rn4KWD5L0P2z