Abstract Class Vs Interface

Feature	Interface	Abstract class
Multiple inheritance	A class may inherit several  interface .	A class may inherit only one  abstract class .
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.
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
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.
Homogeneity	If various implementations only share method signatures then it is better to use interface	If various implementations are of the same kind and use common behaviour or status then abstract class  is better to use.
Speed	Requires more time to find the actual method in the corresponding classes.	Fast
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.
Fields and Constants	No fields can be defined in interfaces	An  abstract class can have fields and constrants defined.