Difference between abstract class and interface

Answer Posted / poulami

Interface vs. Abstract class

1.Multiple inheritance

A class may inherit several interfaces.
A class may inherit only one abstract class.

2.Default implementation

An interface cannot provide any code, just the signature.
An abstract class can provide complete, default code and/or
just the details that have to be overridden.

3.Access Modfiers

An interface cannot have access modifiers for the subs,
functions, properties etc everything is assumed as public
An abstract class can contain access modifiers for the subs,
functions, properties

4.Core VS Peripheral

Interfaces are used to define the peripheral abilities of a
class. In other words both Human and Vehicle can inherit
from a IMovable interface.
An abstract class defines the core identity of a class and
there it is used for objects of the same type.

5.Homogeneity

If various implementations only share method signatures then
it is better to use Interfaces.
If various implementations are of the same kind and use
common behaviour or status then abstract class is better to use.

6.Speed

Requires more time to find the actual method in the
corresponding classes.
Abstrct classes are fast

7.Adding functionality (Versioning)

If we add a new method to an Interface then we have to track
down all the implementations of the interface and define
implementation for the new method.
If we add a new method to an abstract class then we have the
option of providing default implementation and therefore all
the existing code might work properly.

8.Fields and Constants

No fields can be defined in interfaces
An abstract class can have fields and constrants defined

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