Demystifying the Internal Workings of HashMap and Its Java 8 Extension

source : javaconceptoftheday.com

Introduction:
HashMap is a fundamental data structure in Java, widely used for storing key-value pairs. In this comprehensive guide, we will delve into the internal workings of HashMap and explore its extensions introduced in Java 8. Buckle up, as we embark on a journey through the intricacies of this essential data structure.

Understanding HashMap:
At its core, HashMap relies on an array of buckets to store key-value pairs. Each bucket is essentially a linked list that handles collisions. The process of storing and retrieving elements involves two key operations: put() for insertion and get() for retrieval.

Hashing:
The first step in understanding HashMap is hashing. When a key is supplied, the hash code is computed using the key’s hashCode() method. This hash code is then transformed to ensure a more even distribution across the array of buckets. The result is an index within the array where the key-value pair will be stored.

public class MyKey {
    // Assuming key is a simple class with appropriate equals() and hashCode() methods
}

MyKey myKey = new MyKey();
int hash = myKey.hashCode();
int index = hash & (arraySize - 1);