C# : What is the difference between Interface and Abstract Class

Theoretically their are some differences between Abstract Class and Interface which are listed below:

• A class can implement any number of interfaces but a subclass can at most use only one abstract class.
• An abstract class can have non-abstract methods (concrete methods) while in case of interface all the methods has to be abstract.
• An abstract class can declare or use any variables while an interface is not allowed to do so.
• In an abstract class all data member or functions are private by default while in interface all are public, we can’t change them manually.
• In an abstract class we need to use abstract keyword to declare abstract methods while in an interface we don’t need to use that.
• An abstract class can’t be used for multiple inheritance while interface can be used as multiple inheritance.
• An abstract class use constructor while in an interface we don’t have any type of constructor.