Java Collection Set

A Set in Java is a collection of unique elements that does not allow duplicates. It is part of the Java Collections Framework and is useful when uniqueness is required, such as storing IDs, unique names, or distinct elements.

Set Type	Description	Implementation
HashSet	Stores unique elements with no order	HashSet<E>
LinkedHashSet	Maintains insertion order	LinkedHashSet<E>
TreeSet	Maintains elements in sorted order	TreeSet<E>

Using HashSet:

import java.util.HashSet;

import java.util.Set;

public class Main {

public static void main(String[] args) {

Set<String> set = new HashSet<>();

set.add("Apple");

set.add("Banana");

set.add("Cherry");

set.add("Apple"); // Duplicate, ignored

System.out.println(set); // Output: [Banana, Apple, Cherry] (unordered)

}

Try it yourself

Using LinkedHashSet:

import java.util.LinkedHashSet;

import java.util.Set;

public class Main {

public static void main(String[] args) {

Set<String> set = new LinkedHashSet<>();

set.add("Apple");

set.add("Banana");

set.add("Cherry");

System.out.println(set); // Output: [Apple, Banana, Cherry] (insertion order)

}

Try it yourself

Using TreeSet:

import java.util.TreeSet;

import java.util.Set;

public class Main {

public static void main(String[] args) {

Set<Integer> set = new TreeSet<>();

set.add(30);

set.add(10);

set.add(20);

System.out.println(set); // Output: [10, 20, 30] (sorted order)

}

Try it yourself

Set Methods:

Method	Description
add(E e)	Adds an element (ignores duplicates)
remove(E e)	Removes an element
contains(E e)	Checks if an element exists
size()	Returns the number of elements
isEmpty()	Checks if the set is empty
clear()	Removes all elements
iterator()	Returns an iterator to traverse the set

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Set Type

Description

Implementation

Using HashSet:

Using LinkedHashSet:

Using TreeSet:

Set Methods:

Method

Description