What is the default number of buckets used in the HashMap implementation in Java?

By default, the HashMap implementation in Java uses 16 buckets. This means that when creating a new HashMap object without specifying an initial capacity, the internal array of buckets has a size of 16.

Each bucket is a linked list or a tree (starting from Java 8, when there are many collisions), which stores key-value pairs with the same hash modulo the array size.

Example of creating a HashMap with the default size:

HashMap<String, Integer> map = new HashMap<>();
// The internal array of buckets has a size of 16

This value is chosen as a power of two to optimize the calculation of the bucket index using bitwise operations.