Static Class in C#

 A static class is basically the same as a non-static class, but there is one difference: a static class cannot be instantiated. In other words, you cannot use the new keyword to create a variable of the class type. Because there is no instance variable, you access the members of a static class by using the class name itself. For example, if you have a static class that is named UtilityClass that has a public method named MethodA, you call the method as shown in the following example: UtilityClass.MethodA();

 A static constructor is only called one time, and a static class remains in memory for the lifetime of the application domain in which your program resides.

The following list provides the main features of a static class:

• Contains only static members.
• Cannot be instantiated.
• Is sealed.
• Cannot contain Instance Constructors.

Creating a static class is therefore basically the same as creating a class that contains only static members and a private constructor. A private constructor prevents the class from being instantiated. The advantage of using a static class is that the compiler can check to make sure that no instance members are accidentally added. The compiler will guarantee that instances of this class cannot be created.

Static classes are sealed and therefore cannot be inherited. They cannot inherit from any class except Object. Static classes cannot contain an instance constructor; however, they can contain a static constructor. Non-static classes should also define a static constructor if the class contains static members that require non-trivial initialization.

Static methods can be overloaded but not overridden, because they belong to the class, and not to any instance of the class.

public static class TemperatureConverter

{

    public static double CelsiusToFahrenheit(string temperatureCelsius)

    {

        // Convert argument to double for calculations.

        double celsius = Double.Parse(temperatureCelsius);

        // Convert Celsius to Fahrenheit.

        double fahrenheit = (celsius * 9 / 5) + 32;

        return fahrenheit;

    }

    public static double FahrenheitToCelsius(string temperatureFahrenheit)

    {

        // Convert argument to double for calculations.

        double fahrenheit = Double.Parse(temperatureFahrenheit);

        // Convert Fahrenheit to Celsius.

        double celsius = (fahrenheit - 32) * 5 / 9;

        return celsius;

    }

}

class TestTemperatureConverter

{

    static void Main()

    {

        Console.WriteLine("Please select the convertor direction");

        Console.WriteLine("1. From Celsius to Fahrenheit.");

        Console.WriteLine("2. From Fahrenheit to Celsius.");

        Console.Write(":");

        string selection = Console.ReadLine();

        double F, C = 0;

        switch (selection)

        {

            case "1":

                Console.Write("Please enter the Celsius temperature: ");

                F = TemperatureConverter.CelsiusToFahrenheit(Console.ReadLine());

                Console.WriteLine("Temperature in Fahrenheit: {0:F2}", F);

                break;

            case "2":

                Console.Write("Please enter the Fahrenheit temperature: ");

                C = TemperatureConverter.FahrenheitToCelsius(Console.ReadLine());

                Console.WriteLine("Temperature in Celsius: {0:F2}", C);

                break;

            default:

                Console.WriteLine("Please select a convertor.");

                break;

        }

        // Keep the console window open in debug mode.

        Console.WriteLine("Press any key to exit.");

        Console.ReadKey();

    }

} 

 Example Output:

    Please select the convertor direction

    1. From Celsius to Fahrenheit.

    2. From Fahrenheit to Celsius.  :2

    Please enter the Fahrenheit temperature: 20

    Temperature in Celsius: -6.67

    Press any key to exit.