Java HashSet

In Java, the HashSet is a collection that is part of the java.util package. It is used to store unique elements in an unordered way and is backed by a HashMap. This post by The Coding College will cover the key features, syntax, methods, and examples of HashSet, ensuring that we follow Google E-E-A-T principles for user benefit.

What is a HashSet?

A HashSet is a collection that implements the Set interface. It is used to store elements where duplication is not allowed. HashSet uses hashing to provide fast insertion, deletion, and lookup operations.

Key Features of HashSet

  1. Unique Elements: Only unique elements are allowed. Duplicate values are ignored.
  2. Unordered: HashSet does not maintain the insertion order of elements.
  3. Fast Performance: HashSet offers constant time (O(1)) performance for basic operations like add, remove, and contains.
  4. Allows Null: Only one null value can be stored in a HashSet.
  5. Not Synchronized: HashSet is not thread-safe but can be synchronized externally if needed.

How to Use HashSet

To use a HashSet in Java, you must import the java.util.HashSet package.

Syntax:

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

Example: Creating a Simple HashSet

Code:

import java.util.HashSet;

public class Main {
    public static void main(String[] args) {
        // Create a HashSet
        HashSet<String> fruits = new HashSet<>();

        // Add elements to the HashSet
        fruits.add("Apple");
        fruits.add("Banana");
        fruits.add("Cherry");
        fruits.add("Apple"); // Duplicate, will be ignored

        // Print the HashSet
        System.out.println("Fruits: " + fruits);
    }
}

Output:

Fruits: [Banana, Cherry, Apple]

Common HashSet Methods

Here are some commonly used methods of the HashSet class:

MethodDescription
add(element)Adds an element to the HashSet.
remove(element)Removes the specified element from the HashSet.
contains(element)Checks if the HashSet contains the specified element.
size()Returns the number of elements in the HashSet.
isEmpty()Checks if the HashSet is empty.
clear()Removes all elements from the HashSet.
iterator()Returns an iterator for the HashSet.

Example: HashSet Operations

Code:

import java.util.HashSet;

public class Main {
    public static void main(String[] args) {
        HashSet<Integer> numbers = new HashSet<>();

        // Add numbers to the HashSet
        numbers.add(10);
        numbers.add(20);
        numbers.add(30);

        // Check if a number exists
        System.out.println("Contains 20? " + numbers.contains(20));

        // Remove a number
        numbers.remove(10);
        System.out.println("HashSet after removal: " + numbers);

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

        // Iterate through the HashSet
        System.out.println("HashSet elements:");
        for (int num : numbers) {
            System.out.println(num);
        }
    }
}

Output:

Contains 20? true
HashSet after removal: [20, 30]
Size of HashSet: 2
HashSet elements:
20
30

HashSet vs Other Sets

FeatureHashSetTreeSetLinkedHashSet
OrderingNo specific orderSorted orderInsertion order
Null ElementsAllows one nullDoes not allow nullAllows one null
PerformanceFast (O(1))Slower (O(log n))Slightly slower

Real-Life Applications of HashSet

  1. Removing Duplicates: HashSet is commonly used to eliminate duplicate elements from a collection.
  2. Quick Lookups: It is used for membership testing or searching elements efficiently.
  3. Storing Unique IDs: Ideal for storing unique identifiers such as student IDs, user IDs, etc.

Conclusion

The HashSet in Java is a powerful tool for working with collections of unique elements. Its performance and simplicity make it an essential component in Java development. For more Java tutorials and coding insights, visit The Coding College and explore our beginner-friendly resources!

Leave a Comment