Explain the concept of Bucket within the HashMap data structure.

In Java's HashMap data structure, a "bucket" is an element of the internal array where all key-value pairs with the same hash index are stored.

When a collision occurs (different keys have the same hash or index), all such elements are placed in one bucket. Previously, a bucket was implemented as a linked list, but starting from Java 8, if many elements fall into a bucket, it is converted into a balanced tree (TreeNode) to speed up search.

Example:

• Compute the hash of the key and find the index in the buckets array.
• If the bucket is empty, place the key-value pair there.
• If not, add it to the linked list or tree within that bucket.

Thus, a bucket is a container for elements with the same index, ensuring storage and search during collisions.