What are Access Modifiers? Explain private, public, protected, internal, protected internal access modifiers.

Access modifiers in C# are keywords that determine the visibility and accessibility of classes, methods, properties, fields, and other members within a program. They control which parts of your code can be accessed from other parts of the program and from outside sources.

There are several access modifiers in C#:

1. public: Members with this modifier are accessible from any part of the program, including outside the class or assembly.

   
   public class PublicExample
   {
       public int PublicField; // Accessible from anywhere
       
       public void PublicMethod()
       {
           Console.WriteLine("This method is public.");
       }
   }
   
   class Program
   {
       static void Main(string[] args)
       {
           PublicExample example = new PublicExample();
           example.PublicField = 42; // Can be accessed directly
           example.PublicMethod(); // Can be called from anywhere
       }
   }
   

2. private: Members with this modifier are only accessible within the same class or struct. They can't be accessed from outside.

   	
   public class PrivateExample
   {
       private int PrivateField; // Accessible only within this class
       
       private void PrivateMethod()
       {
           Console.WriteLine("This method is private.");
       }
   }
   
   class Program
   {
       static void Main(string[] args)
       {
           PrivateExample example = new PrivateExample();
           // example.PrivateField = 42; // This will result in a compile-time error
           // example.PrivateMethod(); // This will result in a compile-time error
       }
   }
   

3. protected: Members with this modifier are accessible within the same class, as well as in derived classes (subclasses). They can't be accessed from outside the class hierarchy.

   		
   public class Parent
   {
       protected int ProtectedField; // Accessible within this class and derived classes
       
       protected void ProtectedMethod()
       {
           Console.WriteLine("This method is protected.");
       }
   }
   
   public class Child : Parent
   {
       public void AccessProtectedMember()
       {
           ProtectedField = 42; // Accessible in derived class
           ProtectedMethod(); // Accessible in derived class
       }
   }
   

4. internal: Members with this modifier are accessible within the same assembly (a compiled unit of code, like a DLL or EXE).

   	
   // Assembly A
   [assembly: InternalsVisibleTo("AssemblyB")]
   
   public class InternalExample
   {
       internal int InternalField; // Accessible within the same assembly
       
       internal void InternalMethod()
       {
           Console.WriteLine("This method is internal.");
       }
   }
   
   // Assembly B
   class Program
   {
       static void Main(string[] args)
       {
           InternalExample example = new InternalExample();
           example.InternalField = 42; // Accessible in the same assembly
           example.InternalMethod(); // Accessible in the same assembly
       }
   }
   

5. protected internal: This is a combination of the protected and internal modifiers. It allows access within the same assembly and in derived classes, whether they are in the same assembly or a different one.

   	
   public class Parent
   {
       protected internal int ProtectedInternalField; // Accessible within this assembly and derived classes
       
       protected internal void ProtectedInternalMethod()
       {
           Console.WriteLine("This method is protected internal.");
       }
   }
   
   class Program
   {
       static void Main(string[] args)
       {
           Parent parent = new Parent();
           parent.ProtectedInternalField = 42; // Accessible in the same assembly
           parent.ProtectedInternalMethod(); // Accessible in the same assembly
       }
   }
   

Access modifiers play a crucial role in encapsulation, which is a principle of object-oriented programming that focuses on controlling the visibility of class members. By specifying the appropriate access modifier, you can manage how much of your code is exposed and accessible to other parts of the program, helping to maintain code organization and security.

Why we use Access Modifiers?

Access modifiers are used in programming languages like C# to control the visibility and accessibility of class members (fields, methods, properties, etc.). They serve several important purposes in software development:

1. Encapsulation: Access modifiers help enforce the principle of encapsulation, which is a fundamental concept in object-oriented programming. Encapsulation means bundling the data (fields) and the methods that operate on the data (methods) into a single unit (class), and controlling the access to that unit. Access modifiers allow you to restrict access to certain members, preventing unintended modifications and ensuring that data is only manipulated through controlled methods.
2. Data Hiding: By making certain members private, you hide the internal implementation details of a class from the outside world. This prevents external code from directly modifying the internal state of an object and helps maintain data integrity and consistency.
3. Abstraction: Access modifiers allow you to define a public interface for a class while keeping its internal details hidden. This way, you can provide a clear and well-defined set of functionalities to users of your class without exposing the complexities of its implementation.
4. Code Organization and Readability: Using access modifiers helps you organize your code by clearly indicating which members are meant to be used by other classes and which are meant to be internal. This improves code readability and makes it easier for other developers (including your future self) to understand and work with your codebase.
5. Security: Access modifiers contribute to the security of your code. By restricting access to sensitive parts of your code, you reduce the risk of unauthorized or accidental modifications that could lead to bugs or security vulnerabilities.
6. Maintenance and Refactoring: Access modifiers make it easier to maintain and refactor your code. When you want to make changes to the internal implementation of a class, you can be confident that external code relying on that class's public interface won't be affected as long as you maintain backward compatibility.
7. Inheritance and Polymorphism: Access modifiers play a role in inheritance and polymorphism. For example, the 'protected' modifier allows derived classes to access certain members of their base class, facilitating code reuse and extension.

In summary, access modifiers help you design and build more robust, secure, and maintainable software by controlling the way different parts of your codebase interact with each other and with external components. They are a crucial tool in achieving the principles of object-oriented programming such as encapsulation, abstraction, and separation of concerns.

Here's the chart about the scope of the accessibility of access modifiers: