What’s the difference between an interface and abstract class?

Feature	Interface	Abstract class
Multiple inheritance	A class may inherit several interfaces.	A class may inherit only one abstract class.
Default implementation	All methods are abstract  there is no implementation	An abstract class can provide complete, default code and/or just the details that have to be overridden.
Constants	Only Static final constants.	Both instance and static constants are possible.
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 the various implementations only share method signatures then it is better to use Interface.	If the 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	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.
Modifiers	No accessibility modifiers are allowed.	May have accessibility modifiers.