Difference between abstract classes and interfaces in C#

Abstract Classes

- In abstract class a method must be declared as abstract
- For abstract methods there will be no body
- The Abstract methods can delare with Access modifiers(public,internal,protected etc)But when implementing in subclass same access modifier we have to use.
- The Abstract class can contain variables and concrete methods
- Multiple inheritance is not possible
- must and should call all the abstract methods in the derived class
- To implement abstract method in derived class we have to use override keyword
- The accessmodifiers and return types(like void,int etc) must be same in abstract method and in derived class method
- we cannot create an object to abstract classes


Interfaces

- For interface methods also there will be no body
- In Interfaces we cannot use any access modifiers.By default these methods are public.
- We cannot declare variables and concrete methods in interfaces
- Multiple inheritance is possible
- must and should call all the interface methods in the derived class
- To implement interface methods in derived class no need of override keyword
- The accessmodifiers and return types(like void,int etc) must be same in interface methods and in derived class methods
- we cannot create an object to interfaces