C# – Abstract Class vs Interface

	Abstract Class	Interface
Multiple inheritance	Doesn’t support	support
Data Member	contains	Doesn’t contain
Constructor declaration	contains	Doesn’t contain
Definition	May contain definition with no implementation	Just a pattern, an empty shell
Methods	Can have both abstract & non-abstract methods	Can only have abstract methods
Implementation	Can contain both definition and its implementation Incomplete class, cannot be instantiated	Can only have the signature of the functionality without any code
Access Modifier	Can have all access modifiers for member declaration of functions, subs and properties.	Not allowed (all methods must be implicitly defined as public). All the members assumed as implicitly public.
Homogeneity	is used for implementations of the same type, behavior and status	Is used for implementations that share only method signatures
Declaration	Acts as a base class for all other classes, can declare/ use any variable	Not allowed to declare any variables
Core vs Peripheral	Core identity of a class & for objects of the same data type	Used to define Peripheral ability of a class
Rigid vs Supple	More supple	More rigid
Fields definition	Predefined fields & constants	Fields cannot be defined in interfaces

Author: learnwithsomayeh