Principles of OOPS

There are Four Main Principals of OOPS which are called Polymorphism, Data Abstraction, Inheritance and Encapsulation.

Polymorphism

Polymorphism is another strong feature of OOPS. It means one term in many forms. This ability of different objects to respond, each in its own way, to identical messages is called polymorphism. Method Overloading and Overriding are a part of the Polymorphism principle.

Another article has Polymorphism Explained in detail.

Data Abstraction

Abstraction: An abstract class is a parent class that allows inheritance but can never be instantiated. Abstract classes contain one or more abstract methods that do not have implementation. These abstract methods can be defined in the derived class.

Inheritance

Inheritance feature offers to derive a new class from an existing one and acquire all the feature of the existing class. The new class which get the feature from existing class called derived class and other class is called base class.

A detailed dicussion of Inheritance in .NET is given here.

Encapsulation

Binding the data and function in a unit called class is called a data Encapsulation. This allow the user to hide the information for outside world and doesn't allow the other user to change or modify the internal values of class.

Encapsulation is the hiding of data implementation by restricting access to accessors and mutators.

accessors

a get method is an example of accessor.

mutators

set method is an example of mutators.