C# Nested Class

In C#, a class can be defined within another class, which is called a nested class. A nested class can be private or protected, which means it is only accessible from the containing class or from derived classes.

Why use nested classes?

Nested classes are useful when a class has a close relationship with another class and is not useful outside of that relationship. By making it a nested class, you can encapsulate it within the parent class and make it easier to manage.

Syntax

The syntax for defining a nested class is similar to that of a regular class, but with an additional keyword:

1class OuterClass
2{
3    // ...
4    class NestedClass
5    {
6        // ...
7    }
8}

Accessing a nested class

To access a nested class, you need to qualify its name with the name of the containing class:

1OuterClass.NestedClass nestedObj = new OuterClass.NestedClass();

Example

Here is an example of a nested class:

1using System;
2
3public class Program
4{
5    class Calculator
6    {
7        public int Add(int x, int y)
8        {
9            return x + y;
10        }
11
12        public int Subtract(int x, int y)
13        {
14            return x - y;
15        }
16
17        public class ScientificCalculator
18        {
19            public double Power(int x, int y)
20            {
21                return Math.Pow(x, y);
22            }
23        }
24    }
25
26    public static void Main()
27    {
28        Calculator.ScientificCalculator sciCalc = new Calculator.ScientificCalculator();
29        double result = sciCalc.Power(2, 3);
30        Console.WriteLine("2 to the power of 3 is " + result);
31    }
32}

In this example, the Calculator class has a nested ScientificCalculator class. We create an instance of ScientificCalculator and use it to calculate the power of 2 to 3.