Java HashMap is a class that implements the Java Map interface and provides a hash table-based implementation for storing key-value pairs. It allows for efficient lookups, insertions, and deletions of elements based on their keys. Java HashMap is part of the Java Collections Framework and supports null values and keys, although only one null key is allowed. Introduced in Java 1995 with Java 1.2, HashMap is widely used for storing and manipulating data in an unordered collection.

https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html