Saturday, 1 February 2014

Access modifier in C#

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Access modifiers are an integral part of object-oriented programming. They support the concept of encapsulation, which promotes the idea of hiding functionality. Access modifiers allow you to define who does or doesn't have access to certain features.

In C# there are 5 different types of Access Modifiers.
Modifier
Description
public
There are no restrictions on accessing public members.
private
Access is limited to within the class definition. This is the default access modifier type if none is formally specified
protected
Access is limited to within the class definition and any class that inherits from the class
internal
Access is limited exclusively to classes defined within the current project assembly
protected internal
Access is limited to the current assembly and types derived from the containing class. All members in current project and all members in derived class can access the variables.


Public Modifiers: 
The public keyword is an access modifier for types and type members. Public access is the most permissive access level.

There are no restrictions on accessing public members.

Accessibility: 
  • Can be accessed by objects of the class
  • Can be accessed by derived classes
Example: In the following example num1 is direct access.

using System;
namespace AccessModifiers
{
    class Program
    {
        class AccessMod
        {
            public int num1;
        }
        static void Main(string[] args)
        {
            AccessMod ob1 = new AccessMod();
            //Direct access to public members
            ob1.num1 = 100;
            Console.WriteLine("Number one value in main {0}", ob1.num1);
            Console.ReadLine();
        }
    }
}
Private Modifiers:

Private access is the least permissive access level.

Private members are accessible only within the body of the class or the struct in which they are declared.

Accessibility: 
  • Cannot be accessed by object
  • Cannot be accessed by derived classes
Example: In the following example num2 is not accessible outside the class.

using System;
namespace AccessModifiers
{
    class Program
    {
        class AccessMod
        {
            public int num1;
            int num2;
        }
        static void Main(string[] args)
        {
            AccessMod ob1 = new AccessMod();
            //Direct access to public members
            ob1.num1 = 100;
            //Access to private member is not permitted
            ob1.num2 = 20;
            Console.WriteLine("Number one value in main {0}", ob1.num1);
            Console.ReadLine();
        }
    }
}



The above program will give compilation error, as access to private is not permissible. In the below figure you can see the private member num2 is not available.

private.jpg

Protected Modifiers:
A protected member is accessible from within the class in which it is declared, and from within any class derived from the class that declared this member.

A protected member of a base class is accessible in a derived class only if the access takes place through the derived class type.

Accessibility: 
  • Cannot be accessed by object
  • By derived classes
using System;
namespace AccessModifiers
{
    class Program
    {
        class Base
        {
            protected int num1;
        }
        class Derived : Base
        {
            public int num2;
            static void Main(string[] args)
            {
                Base ob1 = new Base();
                Derived ob2 = new Derived();
                ob2.num1 = 20;
                // Access to protected member as it is inhertited by the Derived class
                ob2.num2 = 90;
                Console.WriteLine("Number2 value {0}", ob2.num2);
                Console.WriteLine("Number1 value which is protected {0}", ob2.num1);
                Console.ReadLine();
            }
        }
    }
}



In the above program we try to access protected member in main it is not available as shown in the picture below that num1 is not listed in intellisense.

protected.jpg

internal modifier 

The internal keyword is an access modifier for types and type members. We can declare a class as internal or its member as internal. Internal members are accessible only within files in the same assembly (.dll).

In other words, access is limited exclusively to classes defined within the current project assembly.

Accessibility:

In same assembly (public) 
  • Can be accessed by objects of the class
  • Can be accessed by derived classes
In other assembly (internal) 
  • Cannot be accessed by object
  • Cannot be accessed by derived classes
protected internal 

The protected internal accessibility means protected OR internal, not protected AND internal.

In other words, a protected internal member is accessible from any class in the same assembly, including derived classes.

The protected internal access modifier seems to be a confusing but is a union of protected and internal in terms of providing access but not restricting. It allows:  
  • Inherited types, even though they belong to a different assembly, have access to the protected internal members.
  • Types that reside in the same assembly, even if they are not derived from the type, also have access to the protected internal members.

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