References:

Objects -> https://docs.oracle.com/javase/tutorial/java/concepts/object.html

Class -> https://docs.oracle.com/javase/tutorial/java/concepts/class.html

OOP fundamental Concept -> https://keremkosaner.wordpress.com/2007/05/03/oop-fundamental-concepts/

Identifier -> https://en.wikipedia.org/wiki/Identifier

Naming Convention -> https://en.wikipedia.org/wiki/Naming_convention_(programming)

Java package -> https://en.wikipedia.org/wiki/Java_package