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How does HashMap internally works? Explain about this in detail. 

A HashMap is a data structure that stores data in key-value pairs and allows fast access to values using their keys. Here’s how it works in a simple way:

1: Hashing the Key

When you put a key-value pair into the HashMap, it uses a special function called a hash function to convert the key into a number (called a hash code).

2: Index Calculation

The hash code is used to find an index in an internal array (called a bucket array). This index tells HashMap where to store the value.

3: Storing the Entry

The value (along with the key) is stored at the calculated index in the array.

4: Handling Collisions

Sometimes, two different keys can get the same index (this is called a collision). When this happens, HashMap stores both entries at the same index using a linked list or a tree structure.

5: Retrieving Values

When you ask for a value using a key, HashMap hashes the key again, finds the correct index, and looks for the key in that spot. If it finds the key, it returns the value.

6: Efficiency

Because it uses the hash function and direct indexing, HashMap operations (like get and put) are usually very fast (close to constant time).

In summary:

1: HashMap uses a hash function to quickly find where to store or find data, making it very efficient for looking up values by keys.

2: Here’s a step-by-step explanation of how HashMap works, and I can visualize this as a diagram for you.

Text Explanation

-> Key is given to HashMap.

-> HashMap calculates the hash code for the key.

-> Hash code is used to find the index in the internal array (bucket).

-> The key-value pair is stored at that index.

-> If two keys have the same index (collision), they are stored together using a linked list or tree.

-> When searching for a value, HashMap hashes the key, finds the index, and retrieves the value.