Java HashMap.size() is a method in the Java HashMap class that returns the number of key-value pairs in the map. It is often used to determine the size of the map before performing operations like iteration or checking for capacity limits. Introduced in Java 1995 with Java 1.2, size() is commonly used for managing collections of key-value pairs and performing efficiency checks in Java applications.

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