When should you prefer HashSet and when should you avoid it?

HashSet is a part of Java's collection framework and is used to store unique elements. It implements the Set interface and is backed by a hash table. While it offers efficiency in certain scenarios, there are situations where its use may not be optimal. Below are some guidelines on when to prefer HashSet and when to avoid it.

When to Prefer HashSet:

• Fast Lookup: Use HashSet when you need fast lookup, insertion, and deletion operations. HashSet offers average constant time complexity for these operations.
• Unique Elements: When you need a collection that maintains unique elements and duplicates are not allowed.
• Conditional Filtering: In scenarios where you need to filter out duplicates from a collection, HashSet can be a good choice.

When to Avoid HashSet:

• Ordering of Elements: If the order of elements is important, consider using LinkedHashSet or TreeSet instead, as HashSet does not maintain any order.
• Performance Concern with Large Datasets: In scenarios with very large datasets where memory consumption and hash collisions could lead to performance degradation.
• Custom Objects: If you are storing custom objects, be cautious about overriding the hashCode() and equals() methods; otherwise, it may lead to unexpected behavior.

Example:

import java.util.HashSet;

public class HashSetExample {
    public static void main(String[] args) {
        HashSet set = new HashSet<>();
        set.add("Apple");
        set.add("Banana");
        set.add("Orange");
        set.add("Apple"); // Duplicate element

        // Displaying the unique elements
        for (String fruit : set) {
            System.out.println(fruit);
        }
    }
}