Consider the following UML diagram

You have to implement the code for these classes. Remember Sub$-$classes have to implement the abstract method of super$-$class. Identify and implement it correctly.

Consider the following instructions:

The following variables are considered final

a Publication class: all variables.

b$.$ Author class: Author name and gender.

Validation: Author name must not be null or empty. Ensure consistency in your code and never allow an object to hold invalid data. The class should throw an IllegalArgumentException instance for invalid data.