OOP, or Object-Oriented Programming, is a programming paradigm that is based on the concept of "objects", which can contain data and code that manipulates that data. In OOP, you define "classes" that represent real-world objects, and you create "instances" of those classes to carry out tasks. One of the main benefits of OOP is that it allows developers to create modular and reusable code, which can make it easier to develop and maintain complex software systems. OOP languages include Java, C++, and Python, among others.

Encapsulation is the technique of hiding the properties and method details of an object from outside the class, and providing a controlled interface through which the object can be accessed and manipulated. This act of closing off allows the object to change without affecting the code that uses it. Encapsulation provides a level of security for the internal state of the object by limiting unauthorized access in addition to promoting modularity and reusability of programming.

Here you can see that the Animal class has 2 fields type and legs. Where encapsulation takes place is when we set the keyword private to each object field. The reason why we use the keyword private is to keep other parts outside of the class from using these object fields. This privatization is generally used to allow each object to use their fields as one whole entity. This concept derives itself from the real world. Example, a dog is known to have 4 legs, someone can't just make a dog have 5 legs because 4 legs are attributed to a dog.

With the help of polymorphism, several data types can be handled by a single function or method in object-oriented programming. This enables more adaptable and reuseable code. Polymorphism is the capacity of a single function or method to operate on a variety of data types. Along with inheritance and encapsulation, it is one of the core ideas in object-oriented programming.

Here you can see that the method add() is written twice but one method returns an integer and the other returns a double. This allows the client using this method to be able to perform the same process but with different data types. This idea of taking up multiple forms is know as polymorphism. Another word used with polymorphism is overriding a method.

To abstract away something is to bury the implementation details within something, which can be a prototype or a function. Therefore, you are not required to fully comprehend the function's purpose while calling it. You would never write any code if you had to comprehend every single function in a large codebase. It would take weeks or months to read everything. By removing some details, you can produce a reusable, easily understandable, and adaptable codebase.

When anything has to be extended, an abstract class is used to represent it. Let's imagine that we wish to use an application to model employees and their various job roles. The work that each person performs depends on their position, even if we are aware that each employee will have a name and be a part of a department. We may create a class called Employee and is used for specific employment positions that extend Employee to simulate this scenario. To require implementation from subclasses, we can make the Employee class abstract and define an abstract method inside of it.

In another Java file we can create another class called developer and extend the Employee class. In a real world perspective we can represent this concept abstractly like this.

Inheritance is a concept in object-oriented programming (OOP) where a class (called the child class or subclass) inherits the properties and methods of another class (called the parent class or superclass). This allows you to reuse and organize your code, as well as the ability to model real-world relationships between different objects. The child class can also add or override properties and methods of the parent class.

A good example of inheritance would be the image above this. The Developer class inherits the Employee super class.