What is a Static Constructor in C#?
💡 Concept: Static Constructor
A static constructor in C# is used to initialize static fields of a class or to perform actions that only need to be done once, regardless of the number of class instances.
📘 Quick Intro
Static constructors are special methods without parameters that initialize static data members. They are called automatically before the first instance is created or any static member is accessed.
🧠 Analogy
Think of a static constructor like setting up the stage before the first act in a play. It prepares everything once, before any actors (objects) come on stage.
🔧 Technical Explanation
- 🔹 Static constructors do not take parameters and cannot be overloaded.
- 🔹 They are called automatically before any static members are accessed.
- 🔹 Only one static constructor per class is allowed.
- 🔹 You cannot call a static constructor explicitly.
- 🔹 Useful for initializing static variables and performing one-time operations.
🎯 Use Cases
- ⚡ Initializing static variables that require logic.
- 🔐 Setting up logging or configuration settings.
- 🛠 Preparing resources or file paths before usage.
- 📦 Enforcing one-time setup for Singleton patterns.
💻 Code Example
public class Config
{
public static string AppName;
// Static Constructor
static Config()
{
Console.WriteLine("Static constructor called.");
AppName = "FullStackPrep.Dev";
}
}
class Program
{
static void Main()
{
Console.WriteLine(Config.AppName); // Triggers static constructor
}
}
❓ Interview Q&A
Q1: What is a static constructor?
A: A constructor that initializes static data and runs once for the type.
Q2: When is a static constructor called?
A: Automatically before any static members are accessed.
Q3: Can a static constructor take parameters?
A: No, they must be parameterless.
Q4: Can you overload a static constructor?
A: No, only one is allowed per class.
Q5: Is it mandatory to define a static constructor?
A: No, it’s optional and used when needed.
Q6: Can you call a static constructor directly?
A: No, it’s invoked automatically.
Q7: Can a static constructor access instance members?
A: No, only static members can be accessed.
Q8: How often is a static constructor called?
A: Exactly once for the type.
Q9: Is thread safety guaranteed in static constructors?
A: Yes, the runtime ensures it runs only once.
Q10: Can static constructors throw exceptions?
A: Yes, but the type becomes unusable after that.
📝 MCQs
Q1. When is a static constructor called?
- When the program starts
- Before instance is created
- Before any static member is accessed
- After all instances
Q2. How many static constructors can a class have?
- Multiple
- None
- Only one
- Depends on overloads
Q3. Can static constructors be overloaded?
- Yes
- No
- Only if private
- Depends on parameters
Q4. Can you pass arguments to a static constructor?
- Yes
- No
- Optional only
- Through config file
Q5. What is true about static constructors?
- Called manually
- Only for inheritance
- They are invoked automatically
- Cannot use them in interfaces
Q6. Can static constructors be inherited?
- Yes
- No
- Only with virtual keyword
- Only in sealed classes
Q7. Can static constructors initialize static fields?
- No
- Only instance
- Yes
- Sometimes
Q8. Do static constructors have return types?
- Yes
- No
- Void
- Static
Q9. Are static constructors thread-safe?
- No
- Only in .NET 5+
- Yes, by CLR
- Only when locked
Q10. Can a class have both static and instance constructors?
- No
- Yes
- Only if sealed
- Only with overloads
💡 Bonus Insight
Use static constructors wisely to ensure one-time setup of static members. Avoid logic that can fail—any unhandled exception prevents the class from being used.
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