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C# Abstraction


C# Abstract Classes and Methods

Data abstraction is the process of hiding certain details and showing only essential information to the user.
Abstraction can be achieved with either abstract classes or interfaces (which you will learn more about in the next chapter).

The abstract keyword is used for classes and methods:

  • Abstract class: is a restricted class that cannot be used to create objects (to access it, it must be inherited from another class).

  • Abstract method: can only be used in an abstract class, and it does not have a body. The body is provided by the derived class (inherited from).

An abstract class can have both abstract and regular methods:

abstract class Animal {
  public abstract void animalSound();
  public void sleep() {
    Console.WriteLine("Zzz");
  }
}

From the example above, it is not possible to create an object of the Animal class:

Animal myObj = new Animal(); // Will generate an error (Cannot create an instance of the abstract class or interface 'Animal')

To access the abstract class, it must be inherited from another class. Let's convert the Animal class we used in the Polymorphism chapter to an abstract class.

Remember from the Inheritance chapter that we use the : symbol to inherit from a class, and that we use the override keyword to override the base class method.

Example

// Abstract class
abstract class Animal
{
  // Abstract method (does not have a body)
  public abstract void animalSound();
  // Regular method
  public void sleep()
  {
    Console.WriteLine("Zzz");
  }
}

// Derived class (inherit from Animal)
class Pig : Animal
{
  public override void animalSound()
  {
    // The body of animalSound() is provided here
    Console.WriteLine("The pig says: wee wee");
  }
}

class Program
{
  static void Main(string[] args)
  {
    Pig myPig = new Pig(); // Create a Pig object
    myPig.animalSound();  // Call the abstract method
    myPig.sleep();  // Call the regular method
  }
}

Run example »

Why And When To Use Abstract Classes and Methods?

To achieve security - hide certain details and only show the important details of an object.

Note: Abstraction can also be achieved with Interfaces, which you will learn more about in the next chapter.