Thursday, April 8, 2010

Difference between abstract class and interface

What is an Abstract Class?

  1. An abstract class is a special kind of class that cannot be instantiated.So the question is why we need a class that cannot be instantiated? An abstract class is only to be sub-classed (inherited from). In other words, it only allows other classes to inherit from it but cannot be instantiated. The advantage is that it enforces certain hierarchies for all the subclasses. In simple words, it is a kind of contract that forces all the subclasses to carry on the same hierarchies or standards.
  2.  A class may inherit only one abstract class.
  3. An abstract class can contain access modifiers for the subs, functions, properties
  4. Fast
  5. An abstract class can have fields and constants defined

What is an Interface?

  1. An interface is not a class. It is an entity that is defined by the word Interface. An interface has no implementation; it only has the signature or in other words, just the definition of the methods without the body. As one of the similarities to Abstract class, it is a contract that is used to define hierarchies for all subclasses or it defines specific set of methods and their arguments. The main difference between them is that a class can implement more than one interface but can only inherit from one abstract class.
  2. A class may inherit several interfaces.
  3. An interface cannot have access modifiers for the subs, functions, properties etc everything is assumed as public
  4. Requires more time to find the actual method in the corresponding classes.
  5. No fields can be defined in interfaces

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