Difference between Abstract Class and Interface with example.

Question

ICSM · Answer

Both abstract classes and interfaces define 
contracts for other classes to implement, but they differ in capabilities, design purpose, and usage.
Quick Comparison Table
Feature
Abstract Class
Interface
Inheritance
One abstract class per class (single inheritance)
Multiple interfaces can be implemented
Members
Fields, constructors, methods, properties
Only method/property signatures (no fields)
Method implementation
Can have implemented and abstract methods
C# 8.0+: Can have default methods
Access modifiers
Yes (public, protected, etc.)
All members are public by default
Constructors
Yes
No constructors
Use case
Common base with shared code
Only contract definition (pure abstraction)
Performance/Size
Slightly heavier
Lightweight
Example: Abstract Class
public abstract class Animal
{
    public string Name { get; set; }
    public void Eat()
    {
        Console.WriteLine("Animal is eating");
    }
    public abstract void MakeSound(); // must be implemented in derived class
}
public class Dog : Animal
{
    public override void MakeSound()
    {
        Console.WriteLine("Bark!");
    }
}
Usage:
Animal dog = new Dog();
dog.Eat();        // Inherited concrete method
dog.MakeSound();  // Overridden method
Example: Interface
public interface IPlayable
{
    void Play();
}
public interface IStoppable
{
    void Stop();
}
public class MediaPlayer : IPlayable, IStoppable
{
    public void Play() =andgt; Console.WriteLine("Playing...");
    public void Stop() =andgt; Console.WriteLine("Stopped.");
}
Usage:
IPlayable player = new MediaPlayer();
player.Play();
When to Use What?
Scenario
Use
Need to provide base functionality
Abstract class
Need to support multiple base types
Interface
Design a plug-in system or API contract
Interface
Need constructors or fields
Abstract class
Want to share default code
Abstract class (or C# 8+ interfaces)
Tip
Use interface when you only need contract/behaviorUse abstract class when you need to share logic and structure

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Difference between Abstract Class and Interface with example.

Anubhav Kumar

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1 Answers

Quick Comparison Table

Example: Abstract Class

Usage:

Example: Interface

Usage:

When to Use What?

Tip

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Feature	Abstract Class	Interface
Inheritance	One abstract class per class (single inheritance)	Multiple interfaces can be implemented
Members	Fields, constructors, methods, properties	Only method/property signatures (no fields)
Method implementation	Can have implemented & abstract methods	C# 8.0+: Can have default methods
Access modifiers	Yes (public, protected, etc.)	All members are public by default
Constructors	Yes	No constructors
Use case	Common base with shared code	Only contract definition (pure abstraction)
Performance/Size	Slightly heavier	Lightweight

Scenario	Use
Need to provide base functionality	Abstract class
Need to support multiple base types	Interface
Design a plug-in system or API contract	Interface
Need constructors or fields	Abstract class
Want to share default code	Abstract class (or C# 8+ interfaces)