C# - Question on Static Classes

Questions & Answers for Static Classes in C#

1. What is a static constructor in C#?

Answer: A static constructor is a special constructor used to initialize static members of a class. It is called automatically before the first instance is created or any static members are accessed.

Code

public class MyClass
{
    public static int Value;

    static MyClass()
    {
        Value = 10; // Initialize static field
        Console.WriteLine("Static constructor called.");
    }
}

2. Can a static constructor have parameters?

Answer: No, a static constructor cannot have parameters. It is parameterless because it is called by the runtime automatically and cannot be explicitly invoked.

3. When is a static constructor called?

Answer: A static constructor is called:

• Automatically by the runtime.
• Only once per class.
• Before the first access to a static member or before creating an instance of the class.

4. Can a static constructor be overloaded?

Answer: No, a static constructor cannot be overloaded. Each class can only have one static constructor.

5. What is the access modifier of a static constructor?

Answer: A static constructor does not have an access modifier. It is always private and cannot be called directly.

6. What happens if both a static constructor and an instance constructor are present in a class?

Answer: If both are present:

The static constructor is called before the instance constructor, but only once, before any static or instance member is accessed.

public class TestClass
{
    public static int StaticValue;
    public int InstanceValue;

    static TestClass()
    {
        StaticValue = 100;
        Console.WriteLine("Static constructor called.");
    }

    public TestClass()
    {
        InstanceValue = 200;
        Console.WriteLine("Instance constructor called.");
    }
}

class Program
{
    static void Main()
    {
        Console.WriteLine(TestClass.StaticValue); // Static constructor is called here
        var obj = new TestClass(); // Instance constructor is called after
    }
}

Output

Static constructor called.
100
Instance constructor called.

7. Can we explicitly call a static constructor?

Answer: No, a static constructor cannot be called explicitly. It is automatically invoked by the runtime.

8.  Can a static constructor access instance members?

Answer: No, a static constructor cannot access instance members directly because it is not tied to an object instance.

9. Is it possible to define a static constructor in a static class?

Answer: Yes, a static class can have a static constructor. In fact, a static class often uses a static constructor for initialization.

public static class Config
{
    public static string AppName;

    static Config()
    {
        AppName = "My Application";
        Console.WriteLine("Static constructor in static class called.");
    }
}

10. What happens if there is an exception in a static constructor?

Answer: If a static constructor throws an exception:

• The type remains uninitialized.
• Any subsequent attempts to use the type will result in a TypeInitializationException.

public class FaultyClass
{
    static FaultyClass()
    {
        throw new Exception("Error in static constructor");
    }
}

class Program
{
    static void Main()
    {
        try
        {
            var obj = new FaultyClass();
        }
        catch (TypeInitializationException ex)
        {
            Console.WriteLine(ex.Message);
        }
    }
}