C# Abstract Classes

Abstract classes are a fundamental concept in C# and object-oriented programming. They serve as a blueprint for other classes, providing a common structure and behavior while allowing for specialized implementations.

What are Abstract Classes?

An abstract class is a special type of class that cannot be instantiated directly. It's designed to be inherited by other classes, known as concrete classes. Abstract classes can contain both abstract and non-abstract members.

Key Features of Abstract Classes

• Cannot be instantiated
• May contain abstract and non-abstract methods
• Can have constructors and destructors
• Can implement C# Interfaces

Syntax and Usage

To declare an abstract class in C#, use the abstract keyword before the class definition. Here's a basic example:

public abstract class Shape
{
    public abstract double CalculateArea();

    public void Display()
    {
        Console.WriteLine($"Area: {CalculateArea()}");
    }
}
    

In this example, Shape is an abstract class with an abstract method CalculateArea() and a concrete method Display().

Implementing Abstract Classes

To use an abstract class, you must create a derived class that implements all abstract members. Here's an example:

public class Circle : Shape
{
    private double radius;

    public Circle(double r)
    {
        radius = r;
    }

    public override double CalculateArea()
    {
        return Math.PI * radius * radius;
    }
}
    

The Circle class inherits from Shape and provides an implementation for the abstract CalculateArea() method.

When to Use Abstract Classes

Abstract classes are useful in several scenarios:

• When you want to provide a common interface for a group of related classes
• To define a base class that encapsulates common functionality
• When you need to declare non-public members or methods

Abstract Classes vs. Interfaces

While abstract classes and C# Interfaces serve similar purposes, they have key differences:

Abstract Classes	Interfaces
Can have implementation details	Only method signatures (prior to C# 8.0)
Support single inheritance	Support multiple inheritance
Can have constructors	Cannot have constructors

Best Practices

• Use abstract classes to define a common base for a family of related classes
• Implement abstract methods in derived classes using the override keyword
• Consider using interfaces for multiple inheritance scenarios
• Avoid creating deep inheritance hierarchies

Abstract classes play a crucial role in C# Inheritance and Polymorphism. They provide a powerful way to design flexible and extensible class hierarchies in your C# applications.