Abstract classes and interfaces are both fundamental concepts in object-oriented programming that promote code reusability and flexibility. However, they serve distinct purposes:

Abstract Classes:

Purpose:

• Serve as blueprints for derived classes, defining a common foundation.
• Enforce implementation of specific behaviors through abstract methods.
• Offer shared functionality through concrete methods (optional).

Key Features:

• Can contain both abstract and concrete methods.
• Can have constructors and access modifiers (public, private, protected).
• Can hold fields and properties.expand_more
• Classes can only inherit from one abstract class directly.exclamation

Example:

C#:

public abstract class Animal
{
    public abstract void MakeSound(); // Abstract method (must be implemented)
    public virtual void Eat() // Concrete method (can be overridden)
    {
        Console.WriteLine("The animal is eating.");
    }
}

Interfaces:

Purpose:

• Define contracts that classes must adhere to, ensuring consistency.
• Specify a set of functionalities that implementing classes must provide.

Key Features:

• Only contain abstract methods (no implementation).
• Cannot have constructors, fields, or properties.
• Classes can implement multiple interfaces.expand_more

Example:

C#:

public interface IShape
{
    double CalculateArea(); // Abstract method
}

Key Differences Summary:

Feature	Abstract Class	Interface
Purpose	Blueprint for inheritance	Contract for behavior
Methods	Abstract and concrete	Abstract only
Inheritance	Single inheritance	Multiple inheritance
Constructors	Can have constructors	No constructors
Fields/Properties	Can have fields and properties	No fields or properties

When to Use Which:

Abstract Classes:

• When you need to establish a common base for related classes with shared functionality.
• When you want to control implementation details for some methods while allowing flexibility for others.

Interfaces:

• When you want to define a contract across unrelated classes that share specific behaviors.
• When you need loose coupling and flexibility in class design.
• When classes need to adhere to multiple contracts (multiple interface implementation).

Choosing Between Abstract Class and Interface:

• Use an abstract class when you want to define a base class with shared functionalities (concrete methods) and force derived classes to implement specific behaviors (abstract methods).
• Use an interface when you want to define a set of functionalities that various unrelated classes can implement independently.

By understanding these distinctions, you can effectively leverage abstract classes and interfaces to create more robust, reusable, and maintainable object-oriented code in C#.

Here are some helpful resources related to the differences between abstract classes and interfaces in C#, including both explanations and examples:

Official Microsoft Documentation:

• Abstract Classes: https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/abstract
• Interfaces: https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/interface