Hash-Set

HashSet in Java

Overview

The HashSet class in Java is part of the java.util package and implements the Set interface. It uses a hash table for storage and does not allow duplicate elements.

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Characteristics of HashSet

Feature	Details
Package	java.util
Allows Duplicates	No
Maintains Insertion Order	No
Thread-Safe	No
Allows Null Element	Yes

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Key Features of HashSet

• No Duplicates: Ensures that duplicate elements are not allowed.
• Unordered: The order of elements is not guaranteed.
• Fast Access: Offers constant time performance for basic operations like add, remove, and contains (O(1) average time complexity).
• Hash-Based Storage: Internally backed by a HashMap.

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How to Use HashSet

Importing HashSet

import java.util.HashSet;

Creating a HashSet

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

• Example

  HashSet<String> stringSet = new HashSet<>();
  HashSet<Integer> integerSet = new HashSet<>();

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HashSet Specific Methods

The HashSet class provides several methods for efficient set operations. Below are some commonly used methods:

Method	Description	Return Type	Example
add(E e)	Adds the specified element to the set if it is not already present.	boolean	hashSet.add("Apple");
contains(Object o)	Returns true if the set contains the specified element.	boolean	hashSet.contains("Banana");
remove(Object o)	Removes the specified element from the set if it is present.	boolean	hashSet.remove("Apple");
clear()	Removes all elements from the set.	void	hashSet.clear();
isEmpty()	Checks if the set is empty.	boolean	hashSet.isEmpty();
size()	Returns the number of elements in the set.	int	hashSet.size();
toArray()	Converts the set to an array.	Object[]	Object[] array = hashSet.toArray();

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Example Code

import java.util.*;
public class HashSetExample {
    public static void main(String[] args) {
        // Create a HashSet
        HashSet<String> hashSet = new HashSet<>();

        // Add elements
        hashSet.add("Apple");
        hashSet.add("Banana");
        hashSet.add("Cherry");

        // Check size
        System.out.println("Size of the HashSet: " + hashSet.size());

        // Check if an element exists
        System.out.println("Contains 'Banana': " + hashSet.contains("Banana"));

        // Remove an element
        hashSet.remove("Banana");
        System.out.println("HashSet after removal: " + hashSet);

        // Iterate over elements
        System.out.println("HashSet elements:");
        for (String fruit : hashSet) {
            System.out.println(fruit);
        }

        // Convert to array
        Object[] array = hashSet.toArray();
        System.out.println("Array from HashSet: " + Arrays.toString(array));

        // Clear the HashSet
        hashSet.clear();
        System.out.println("Is HashSet empty? " + hashSet.isEmpty());
    }
}

For more: HashSetDataStructure.java