HashSet in Java

HashSet is a part of the Java Collections Framework and is an implementation of the Set interface. It provides a collection that does not allow duplicate elements and has no specific order for its elements. HashSet is based on a hash table data structure, which makes it efficient for adding, removing, and searching for elements in constant time (O(1)) on average.

Declaration and Initialization

To use a HashSet in Java, you need to import the java.util.HashSet package. Here's an example of declaring and initializing a HashSet:

    
import java.util.HashSet;

public class Example {
    public static void main(String[] args) {
        HashSet<String> countries = new HashSet<>();

        // Adding elements to the HashSet
        countries.add("India");
        countries.add("USA");
        countries.add("China");

        // No duplicate elements allowed
        countries.add("India"); // This won't be added

        // Accessing elements
        for (String country : countries) {
            System.out.println(country);
        }

        // Removing elements
        countries.remove("USA");

        // Checking if an element exists
        boolean exists = countries.contains("China");
        System.out.println("China exists in the set: " + exists);
    }
}
   

Common HashSet Operations

Here are some commonly used operations with HashSets:

• add(element): Adds an element to the HashSet.
• remove(element): Removes an element from the HashSet.
• contains(element): Checks if the HashSet contains a specific element.
• size(): Returns the number of elements in the HashSet.
• isEmpty(): Checks if the HashSet is empty.
• clear(): Removes all elements from the HashSet.

HashSet is a widely used data structure when the requirement is to maintain a unique set of elements without any order. It is an excellent choice for tasks that involve checking for existence or eliminating duplicates from a collection of elements.