Key principles

• OOP/Polymorphism is one of the key principles
• What is a OOP/Class
• Why you should use OOP/Composition instead of inheritance
• Always encapsulate (OOP/Encapsulation) your business logic
• Methods/functions are contracts (OOP/Contracts)

Quotes

OO is the ability, through the use of polymorphism, to gain absolute control over every source code dependency in the system. It allows the architect to create a plugin architecture, in which modules that contain high-level policies are independent of modules that contain low-level details. The low-level details are relegated to plugin modules that can be deployed and developed independently from the modules that contain high-level policies. (– )