what are difference between interface and abstract class ?

Shailendra Prasad

22d262OOP/OOD

5 Replies

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Lucas Blake17d ago
The main difference is that an interface defines a contract that a class agrees to follow, while an abstract class can provide both a contract and shared implementation/state. A class can usually implement multiple interfaces, but can inherit from only one abstract class. Which one to use depends on whether you need shared behavior or just a common capability.
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Pankajkumar Patel18d ago

Hi Shailendra Prasad,

Difference between interface and abstract class:

Category	Abstract Class	Interface
What is it?	Abstract doesn’t provide full abstraction.	Interface provides full abstraction.
How to declare/create?	Abstract class is used to create Abstract classes.	Interface is used to create Interfaces.
Can it have fields?	Abstract class can have fields.	Interfaces can’t have fields.
Implementations of its members/methods?	Abstract classes can have implementations for some of their members (methods).	Interface can't have implementation for any of its members.
Access modifiers?	Abstract class members can have access to modifiers.	Interface members can’t have access modifiers.
Default access modifiers?	Abstract class members can be private by default which can be changed.	Interface members can be public by default which can not be changed.
Is it inherited from another Abstract Class or Interface?	Abstract class can inherit from another abstract class or another interface.	Interface can inherit from another interface only and cannot inherit from an abstract class.
Inherit from another Abstract Class or Interface?	Abstract class can inherit from another abstract class or another interface.	Interface can inherit from another interface only and cannot inherit from an abstract class.

Below is one of the best article with complete reference about "difference between interface and abstract class"

Abstract Class Vs Interface in C#

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Sudarshan Hajare18d ago
Interface = a contract. Abstract class = a family.
- Interface says "you must be able to do this" — no implementation, no shared state, and a class can sign up to as many as it wants.
- Abstract class says "you belong to this family" — shared code, shared fields, constructors included, but you can only belong to one.
Quick test: if classes share a capability ? interface. If they share an identity ? abstract class.
Example: Dog, Cat, Human ? all are Mammal ? abstract class.
Dog, Airplane, Superhero ? all can Fly() ? interface.
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Cynthia Sathuragiri18d ago
Both are used for abstraction, but the main difference is:
- Interface is mainly used to define a contract.
- Abstract class can have both abstract methods and common implementation.
- A class can implement multiple interfaces, but can inherit only one abstract class.
- Abstract class can have constructors, fields, properties and implemented methods.
- Interface is useful when different/unrelated classes need to follow the same behavior.
- Abstract class is better when related classes have some common functionality that can be reused.
So, if I need only a contract, I would prefer interface. If I need common logic along with abstraction, I would go with an abstract class.
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Sangeetha S18d ago
Use an Interface when you need to define a contract that multiple unrelated classes can implement. Use an Abstract Class when you want to provide common functionality and shared code for related classes while still forcing derived classes to implement specific behavior.
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