The Hidden Truth About HashSet: How It’s Internally Powered by HashMap

When it comes to choosing between HashMap and HashSet in Java, beginners often get confused. While both are part of the Java Collection Framework and use hashing internally, they serve completely different purposes. In this article, we'll break down the differences in the simplest way possible and even uncover a controversial internal mechanism that many developers overlook!

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1. What is HashMap?

HashMap is a class in Java that implements the Map interface. It stores key-value pairs, meaning every value must be associated with a unique key. The key cannot be duplicated, but values can be.

Key Points:

• Implements Map<K, V> interface.
• Stores data in key-value pairs.
• Keys must be unique, but values can be duplicated.
• Allows null keys and multiple null values.
• Uses hashing for fast retrieval and insertion.

Example:

import java.util.HashMap;

public class HashMapExample {
   
   public static void main(String[] args) {
        HashMap<Integer, String> studentMap = new HashMap<>();
        studentMap.put(1, "Alice");
        studentMap.put(2, "Bob");
        studentMap.put(3, "Charlie");
        studentMap.put(1, "David"); // Overwrites value for key 1
        System.out.println(studentMap); // {1=David, 2=Bob, 3=Charlie}
    }

}

2. What is HashSet?

HashSet is a class in Java that implements the Set interface. It is used to store unique elements, meaning it does not allow duplicates.

Key Points:

• Implements Set<E> interface
• Stores only unique…