C#

OOPS

WHAT IS DIFFERENCE BETWEEN ABSTRACT CLASS , INTERFACE AND VIRTUAL FUNCTION.

VIRTUAL FUNCTION:

By declaring  base class  function as virtual, we allow the function to be overridden in any of derived class.

Example of Virtual Method in .Net:

Class parent
{
virtual void hello()
{

 Console.WriteLine(“Hello from Parent”); }
}

Class child : parent
{
override void hello()
{ Console.WriteLine(“Hello from Child”); }
}

static void main()
{
parent objParent = new child();
objParent.hello();
}

//Output
Hello from Child.

ABSTRACT CLASS:

1.   ABSTRACT CLASS CONTAINS ABSTRACT METHOD AND NON ABSTRACT METHOD

2.   ABSTRACT MEANS ONLY DECLARATION OF METHOD  WITHOUT BODY .  

       eg (public abstract void abstractmethod();) 

     

3    

      3.  ABSTRACT METHOD SHOULD BE OVERRIDDEN  IN DRIVED CLASS WHERE AS            NON ABSTRACT MEMBER IS OPTIONAL.

          EG: 

         4.    ABSTRACT METHOD USE OVERRIDE KEY WORD IN CHILD CLASS.

5             5.  ABSTRACT CLASS CANNOT BE INSTANTIATED.

INTERFACE:

    . INTERFACE IS NOT A CLASS. IT IS AN ENTITY TO DEFINE INTERFACE      KEYWORD.

                 . INTERFACE ONLY CONTAINS ABSTRACT METHOD. AND ALL INTERFACE METHOD SHOULD BE USE IN   DRIVED CLASS

      1   eg:  class sample1

{
  public static void Main()
  {
    System.Console.WriteLine("Hello Interfaces");
  }
}

interface sample
{
  int z;  
}

    output: error Interfaces cannot contain fields

2 eg:class sample2

{
  public static void Main()
  {
    System.Console.WriteLine("Hello Interfaces");
  }
}

interface abc
{
  void test()
  {
     System.Console.WriteLine("test interface");
  }  
}

     output: Interface members cannot have a  definition

    3. 

. INTERFACES ARE IMPLEMENTED, INTERFACE CONTAINS ABSTRACT METHODS BUT WE DON’T HAVE TO DEFINE ABSTRACT KEY WORD.

ü  EG :Interface Sample 
{ 
public void Method1(); 
           void method2(); 
} 

MAIN DIFFERENCE

NOTE: A CLASS CAN IMPLEMENT MULTIPLE INTERFACE BUT A CLASS CANNOT INHERIT MULTIPLE CLASSES (IN .NET WE CAN ACHIEVE MULTIPLE INHERITANCE USING INTERFACE).

ENCAPSULATION:  ability to hide data and behavior that are not necessary to its user. Encapsulation enables a group of properties, methods and other members to be considered a single unit or object.

BY DEFAULT ACCESS SPECIFIERS IS INTERNAL FOR ALL.

·         Public: Access to all code in the program

·         Private: Access to only members of the same class

·         Protected: Access to members of same class and its derived classes

·         Internal: Access to current assembly

·         Protected Internal: Access to current assembly and types derived from containing class