Could you explain the concept of buckets in the implementation of HashMap?

Java's HashMap implementation uses a data structure based on an array of buckets. Each bucket is an array cell that can contain one or more key-value pairs.

When adding an element to the HashMap, the hash code of the key is first computed, then its index in the bucket array is determined (usually by taking the remainder of division by the array size). If the bucket already contains elements (collision), they are stored as a linked list or a tree (starting from Java 8).

Thus, buckets serve to group elements with the same index, which allows efficient searching, adding, and removing of elements by key.

A simplified example:

int bucketIndex = key.hashCode() % buckets.length;
// Add element to buckets[bucketIndex]

If there are many collisions, performance can degrade, so the size of the array and the quality of the hash function are important.