Hello! Today, we'll reinforce our understanding of Object-Oriented Programming (OOP) in Kotlin by revisiting the concepts of Encapsulation, Abstraction, Inheritance, and Polymorphism. Let's dive in!

We'll delve back into OOP. As you may recall, we create objects from classes, which define properties (data) and methods (operations). Also, keep in mind that the keyword this refers to the object whose methods and properties are being accessed.

Here's a refresher:

Now, let's revisit the core principles of OOP: Encapsulation, Abstraction, Inheritance, and Polymorphism.

Encapsulation protects data by making properties private and providing safe methods for access.

Abstraction simplifies systems by creating higher-level representations.

Inheritance allows classes to share properties and methods, promoting code reusability.

Polymorphism enables different types of objects to be handled uniformly if they share some features.

Below is an example demonstrating polymorphism and inheritance:

In this example, Pig, a subclass of Animal, overrides the makeSound method, showcasing polymorphism.

To solidify our understanding, let's examine some practical Kotlin examples.

First, an Employee class showcases encapsulation:

An interface is used to illustrate abstraction:

To sum up, we've reviewed the implementation of the four pillars of OOP in Kotlin — encapsulation, abstraction, inheritance, and polymorphism — and observed these principles in action through demonstrative examples. Our next step is applying this knowledge in the practice session. Happy coding!