Generally, 

Hashmap is used to store the data and it is represented by an object. The main advantage compare with other lists is to give a unique name to each identity to each object.

There are different notations but all are same by means:

Hasmap(KEY,VALUE)

Hashmap(key,value)

Hashmap(K,V)

There are more than 15+ class methods used in hashmap: You can check out here

https://javatutoring.com/java-hashmap-guide/

The above guide will help you out :)

Reg

Mk