Access Specifiers in DotNet

.Net has five access Specifiers:- Defines the accessibility of the types.

                        Public

                        Protected

                        Private

                        Internal

                        protected internal

                 

Public -- Accessible outside the class through object reference.

Private -- Accessible inside the class only through member functions.

Protected -- Just like private but Accessible in derived classes also through member 

functions.

Internal -- Visible inside the assembly. Accessible through objects.

Protected Internal -- Visible inside the assembly through objects and in derived classes outside the assembly through member functions.

Example:-

public class Class1

    {

        int  i;                                         //No Access specifier means private

        public  int j;                                        // Public

        protected int k;                             //Protected data

        internal int m;                        // Internal means visible inside assembly

        protected internal int n;                   //inside assembly as well as to derived classes outside assembly

        static int x;                                 // This is also private

        public static int y;                       //Static means shared across objects

        [DllImport("MyDll.dll")]

        public static extern int MyFoo();       //extern means declared in this assembly defined in some other assembly

        public void myFoo2()

        {

            //Within a class if you create an object of same class then you can access all data members through object reference even private data too

            Class1 obj = new Class1();

            obj.i =10;   //Error can’t access private data through object.But here it is accessible.:)

            obj.j =10;

            obj.k=10;

            obj.m=10;

            obj.n=10;

       //     obj.s =10;  //Errror Static data can be accessed by class names only

            Class1.x = 10;

         //   obj.y = 10; //Errror Static data can be accessed by class names only

            Class1.y = 10;

        }

    }

Now lets try to copy the same code inside Main method and try to compile

[STAThread]

        static void Main()

        {

           //Access specifiers comes into picture only when you create object of class outside the class

            Class1 obj = new Class1();

       //     obj.i =10; //Error can’t access private data through object.

            obj.j =10;

      //      obj.k=10;     //Error can’t access protected data through object.

            obj.m=10;

            obj.n=10;

       //     obj.s =10;  //Errror Static data can be accessed by class names only

            Class1.x = 10;  //Error can’t access private data outside class

         //   obj.y = 10; //Errror Static data can be accessed by class names only

            Class1.y = 10;

        }

What if Main is inside another assembly

[STAThread]

        static void Main()

        {

           //Access specifiers comes into picture only when you create object of class outside the class

            Class1 obj = new Class1();

       //     obj.i =10; //Error can’t access private data through object.

            obj.j =10;

      //      obj.k=10;     //Error can’t access protected data through object.

     //     obj.m=10; // Error can’t access internal data outside assembly

    //      obj.n=10; // Error can’t access internal data outside assembly

       //     obj.s =10;  //Errror Static data can be accessed by class names only

            Class1.x = 10;  //Error can’t access private data outside class

         //   obj.y = 10; //Errror Static data can be accessed by class names only

            Class1.y = 10;

        }

Diffrent between Abstract class and Interface in Asp.Net:-

An Abstract class without any implementation just looks like an Interface; however there are lot of differences than similarities between an Abstract class and an Interface. Let's explain both concepts and compare their similarities and differences.

What is an Abstract Class?

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.

What is an Interface?

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. Since C# doesn't support multiple inheritance, interfaces are used to implement multiple inheritance.

Feature	Interface	Abstract class
Multiple inheritance	A class may inherit several interfaces.	A class may inherit only one abstract class.
Default implementation	An interface cannot provide any code, just the signature.	An abstract class can provide complete, default code and/or just the details that have to be overridden.
Access Modfiers	An interface cannot have access modifiers for the subs, functions, properties etc everything is assumed as public	An abstract class can contain access modifiers for the subs, functions, properties
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 various implementations only share method signatures then it is better to use Interfaces.	If 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 (Versioning)	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.
Fields and Constants	No fields can be defined in interfaces	An abstract class can have fields and constrants defined