Static Classes

Part of the Object Oriented Programming section of Coddy's C# journey — lesson 13 of 70.

When a class contains only static members and you never need to create instances of it, you can declare the entire class as static. This tells the compiler that the class cannot be instantiated and can only contain static members.

public static class MathHelper
{
    public static double Pi = 3.14159;
    
    public static int Square(int number)
    {
        return number * number;
    }
    
    public static int Add(int a, int b)
    {
        return a + b;
    }
}

You use static classes the same way you use static members, by calling them directly on the class name:

int result = MathHelper.Square(5);
double pi = MathHelper.Pi;

Static classes have important restrictions. You cannot create an instance with new, they cannot have instance constructors, and they cannot be inherited. They can only contain static fields, properties, and methods.

The Console and Math classes you've been using are perfect examples of static classes. They provide utility functionality without needing object state. Static classes are ideal for grouping related helper methods or constants that don't require any instance-specific data.

Challenge

Easy

Let's build a temperature conversion utility using a static class to group related helper methods that don't require any object state.

You'll create two files to organize your code:

TemperatureConverter.cs: Define a static class called TemperatureConverter in the Utilities namespace. This class should contain:
- A static field AbsoluteZeroCelsius set to -273.15
- A static method CelsiusToFahrenheit(double celsius) that converts Celsius to Fahrenheit using the formula: (celsius * 9 / 5) + 32
- A static method FahrenheitToCelsius(double fahrenheit) that converts Fahrenheit to Celsius using the formula: (fahrenheit - 32) * 5 / 9
- A static method IsAboveAbsoluteZero(double celsius) that returns true if the temperature is above absolute zero
Program.cs: In your main file, use the static class to perform conversions. Read a temperature value in Celsius from input, then display the conversions and validation.

You will receive one input: a temperature value in Celsius.

Print the results in this format:

{celsius}C = {fahrenheit}F
{fahrenheit}F = {convertedBack}C
Above Absolute Zero: {True/False}
Absolute Zero: {AbsoluteZeroCelsius}C

For example, if the input is 25, the output should be:

25C = 77F
77F = 25C
Above Absolute Zero: True
Absolute Zero: -273.15C

Remember that static classes cannot be instantiated - you'll call all methods directly on the class name like TemperatureConverter.CelsiusToFahrenheit(25).

Cheat sheet

A static class can only contain static members and cannot be instantiated. It's used to group related utility methods and constants that don't require object state.

public static class MathHelper
{
    public static double Pi = 3.14159;
    
    public static int Square(int number)
    {
        return number * number;
    }
    
    public static int Add(int a, int b)
    {
        return a + b;
    }
}

Static class members are accessed directly on the class name:

int result = MathHelper.Square(5);
double pi = MathHelper.Pi;

Restrictions of static classes:

Cannot be instantiated with new
Cannot have instance constructors
Cannot be inherited
Can only contain static fields, properties, and methods

Common examples include Console and Math classes, which provide utility functionality without needing object state.

Try it yourself

using System;
using Utilities;

class Program
{
    public static void Main(string[] args)
    {
        // Read the temperature in Celsius
        double celsius = Convert.ToDouble(Console.ReadLine());
        
        // TODO: Use TemperatureConverter static methods to:
        // 1. Convert celsius to fahrenheit
        // 2. Convert fahrenheit back to celsius
        // 3. Check if temperature is above absolute zero
        // 4. Get the absolute zero constant
        
        // TODO: Print the results in the required format:
        // {celsius}C = {fahrenheit}F
        // {fahrenheit}F = {convertedBack}C
        // Above Absolute Zero: {True/False}
        // Absolute Zero: {AbsoluteZeroCelsius}C
        
    }
}