Nested Classes in C#

A class is a user-defined blueprint or prototype from which objects are created. Basically, a class combines the fields and methods (member function which defines actions) into a single unit. In C#, a user is allowed to define a class within another class. Such types of classes are known as nested class. This feature enables the user to logically group classes that are only used in one place, thus this increases the use of encapsulation, and create more readable and maintainable code.

Syntax:

class Outer_class {

       // Code..

       class Inner_class {

          // Code.. 
       }
}

Example:

Output:

Outer class method
Inner class Method

Important points:

• A nested class can be declared as a private, public, protected, internal, protected internal, or private protected.
• Outer class is not allowed to access inner class members directly as shown in above example.
• You are allowed to create objects of inner class in outer class.
• Inner class can access static member declared in outer class as shown in the below example:

  Example:

  // C# program to illustrate the // concept of nested class accessing // static members of the outer class using System;    // Outer class public class Outer_class {        // Static data member of the outer class     public static string str = "Geeksforgeeks";        // Inner class     public class Inner_class {            // Static method of Inner class         public static void method1()         {                // Displaying the value of a             // static member of the outer class             Console.WriteLine(Outer_class.str);         }     } }    // Driver Class public class GFG {        // Main method     static public void Main()     {            // Accessing static method1          // of the inner class         Outer_class.Inner_class.method1();     } }

  Output :

  Geeksforgeeks

• Inner class can access non-static member declared in outer class as shown in the below example:

  Example:

  // C# program to illustrate the // concept of nested class // accessing non-static member // of the outer class using System;    // Outer class public class Outer_class {        // Non-static data      // member of outer class     public int number = 1000000;        // Inner class     public class Inner_class {            // Static method of Inner class         public static void method1()         {             // Creating the object of the outer class             Outer_class obj = new Outer_class();                // Displaying the value of a              // static member of the outer class             // with the help of obj             Console.WriteLine(obj.number);         }     } }    // Driver Class public class GFG {        // Main method     static public void Main()     {            // Accessing static method1         // of inner class         Outer_class.Inner_class.method1();     } }

  Output :

  1000000

• The scope of a nested class is bounded by the scope of its enclosing class.
• By default, the nested class is private.
• In C#, a user is allowed to inherit a class (including nested class) into another class.

  Example:

  // C# program to illustrate the // concept inheritance using System;    // Outer class public class Outer_class {        // Method of outer class     public void method1()     {         Console.WriteLine("Outer class method");     }        // Inner class     public class Inner_class {     } }    // Derived class public class Exclass : Outer_class {        // Method of derived class     public void func()     {         Console.WriteLine("Method of derived class");     } }    // Driver Class  public class GFG {        // Main method     static public void Main()     {            // Creating object of          // the derived class         Exclass obj = new Exclass();         obj.func();         obj.method1();     } }

  Output :

  Method of derived class
  Outer class method
  

• In C#, the user is allowed to inherit a nested class from the outer class.