How is the HashMap data structure implemented and what happens when adding or searching for elements?

HashMap in Java is implemented based on an array of buckets and linked lists or balanced trees (starting from Java 8) to resolve collisions.

When adding an element:

• The hash code of the key is computed and used to determine the bucket index.
• If the bucket is empty, the element is placed there.
• If the bucket is occupied, the linked list or tree is traversed to find an existing key or add a new element.
• When a certain collision threshold is reached, the linked list is converted into a tree to improve performance.

When searching for an element:

• The hash code of the key is computed and the bucket is determined.
• The list or tree in the bucket is searched by key.
• If the key is found, the associated value is returned.

This approach provides an average complexity of insert and search operations close to O(1), while efficiently handling collisions.