java - What is meant by number of buckets in the HashMap?

Question

I was reading about Hashmap.

An instance of HashMap has two parameters that affect its performance: initial capacity and load factor. The capacity is the number of buckets in the hash table.

If there are 10 key value pairs in the Hashmap. Assume there Hashcode is different.

Each will resides in one bucket right? Or one bucket can have bucket multiple key-value pairs?

Since bucket in english means a big thing where many objects can reside.

Answer 1

Yes, exactly, each bucket can have multiple key-value pairs.

The object's hashCode() determines which bucket it goes into, via this expression: object.hashCode() % n, where n = the total number of buckets and % is the modulus operator.

Most often the objects will be well distributed across buckets, but you have no guarantee where they go. This depends on the data and the hashCode function.

Obviously, when the hashCode implementation is poor, the performance of the hashmap will go down.

Also read up on the equals / hashcode contract, which is relevant.