Difference between Abstract Class and Interface | Abstract Class Vs. Interface

Abstract Class

Interface
Definition An Abstract Class is always used to serve as a base class as it can’t be instantiated. An Interface is one type of template having only signature of methods.
 Type of Methods An Abstract class contains abstract methods and non-abstract (concrete) methods. An Interface contains all abstract methods i.e. all methods have to be abstract.
Default Behavior
 By  Abstract class you can provide default implementation to any method.  By interface you cannot provide default implementation of any method as it only contains signature of methods.
 Multiple Inheritance Any Class can inherit only one Abstract Class so no support for multiple inheritance. Any Class can’t inherit more than one class but it can implement more than one interface.
Object
 You can not create the object of Abstract Class so it must be inherited by other class.  Generally we don’t create the objects of interface we implement the interface in required class.
 Variable You can define & use any variable in abstract class . An Interface does not allow declaration & use of variable as interface does not contain fields.
 Constructor An abstract class can have a constructor. An interface can not have a constructor.
 Inheritance If any class already have a base class, it can not inherit abstract class. Though class have a base class, it can implement any number of interfaces.
 Access Modifiers  An Abstract Class allows to use all access modifiers for the declaration of its members.  An interface does not allow to use any access modifiers for its member declaration and uses public access modifier as default.
 Speed  To access an abstract class is fast than interface. Interface is slower in compare to abstract class.