Mahesh InFO

When working with .NET applications, one of the most common confusions developers face is the difference between Singleton and Static. Both provide global access, but they are not the same thing. In this article, we will dive deep into the definition, usage, and differences between Singleton and Static in .NET with real-world examples.

✅ What is Singleton in .NET?

A Singleton is a design pattern that ensures only one instance of a class is created throughout the application’s lifetime. It provides a global point of access while still following object-oriented principles like inheritance, interfaces, and polymorphism.

Example: Logger Singleton


public sealed class Logger
{
    private static readonly Lazy<Logger> instance =
        new Lazy<Logger>(() => new Logger());

    private Logger() { } // private constructor

    public static Logger Instance => instance.Value;

    public void Log(string message)
    {
        Console.WriteLine($"Log: {message}");
    }
}

Usage:


Logger.Instance.Log("Application started");

👉 Real-world use cases of Singleton:

✅ What is Static in .NET?

A Static class in .NET is a special class that cannot be instantiated. All its members (methods, variables, properties) are static and directly accessible via the class name.

Example: Static Helper Class


public static class MathHelper
{
    public static int Square(int number) => number * number;
}

Usage:


int result = MathHelper.Square(5); // 25

👉 Real-world use cases of Static:

Utility methods (e.g., math calculations, string helpers)
Constants (PI, AppVersion)
Helper classes without state

🔑 Key Differences Between Singleton and Static in .NET

Feature	Singleton	Static
Definition	Design pattern	Language keyword
Object creation	One instance created	No instantiation
Memory lifetime	Managed by Garbage Collector	Lives entire application domain
Supports OOP (Inheritance, Interfaces, Polymorphism)	✅ Yes	❌ No
Thread safety	Needs handling (`lock`, `Lazy<T>`)	CLR ensures thread-safe initialization
State management	Maintains instance state	Global state only
Best use case	Services, configurations, DB connections	Utilities, constants, helper methods

🧠 When to Use Singleton vs Static in .NET

Use Singleton when:
- You need a single object with state.
- You want to implement OOP features like interfaces or inheritance.
- Example: Logging service, configuration manager, database connection.
Use Static when:
- You need stateless utility functions.
- You want a class with only constants or helper methods.
- Example: Math functions, string helpers, conversion utilities.

📌 Final Thoughts

Both Singleton and Static provide global access in .NET, but they solve different problems.

Singleton is best for stateful, OOP-compliant services.
Static is ideal for stateless utility functions and constants.

Choosing the right one depends on whether your requirement involves state + OOP (go for Singleton) or just global utility (go for Static).

In software development, Design Patterns act as proven solutions to common problems. Instead of reinventing the wheel, developers can apply these reusable patterns to build scalable, maintainable, and robust applications.

This article explains Gang of Four (GoF) design patterns and also highlights modern design patterns widely used in cloud, microservices, and enterprise systems.

📌 What Are Design Patterns?

Design patterns are general, reusable solutions to recurring software problems. They are not code snippets but guidelines on how to solve design challenges effectively.

Benefits of using design patterns:

Improve code reusability & readability
Promote best practices & standardization
Reduce development & maintenance time
Help in team communication (common vocabulary)

🏛 Gang of Four (GoF) Design Patterns

The GoF introduced 23 design patterns in their famous book "Design Patterns: Elements of Reusable Object-Oriented Software".

They are categorized into three groups:

1. Creational Patterns – Object creation

Help in creating objects without exposing the creation logic.

Singleton → Ensures only one instance exists.

public sealed class Logger
{
    private static readonly Logger _instance = new Logger();
    private Logger() { }
    public static Logger Instance => _instance;
}

✅ Used in logging, caching, config management.

Factory Method → Subclasses decide object creation.
Abstract Factory → Create families of related objects.
Builder → Step-by-step object construction.
Prototype → Clone objects without depending on their class.

2. Structural Patterns – Class & object composition

Define how objects are composed for flexibility.

Adapter → Converts one interface into another.
✅ Example: Wrapping an old payment gateway API to fit into a new e-commerce app.
Decorator → Add responsibilities dynamically.
Facade → Provide a simple interface to a complex system.
Composite → Treat individual & group objects uniformly (tree structure).
Proxy → Control access (like lazy loading, security).

3. Behavioral Patterns – Object communication

Define how objects interact & responsibilities are distributed.

Observer → One-to-many dependency.

public interface IObserver { void Update(string msg); }
public class User : IObserver
{
    private string _name;
    public User(string name) => _name = name;
    public void Update(string msg) => 
Console.WriteLine($"{_name} got update: {msg}");
}
public class NotificationService
{
    private List<IObserver> observers = new();
    public void Subscribe(IObserver o) => observers.Add(o);
    public void Notify(string msg)
    {
        foreach (var o in observers) o.Update(msg);
    }
}

✅ Used in push notifications, event-driven systems.

Strategy → Choose algorithm at runtime.
Command → Encapsulate actions as objects.
State → Change behavior based on object state.
Mediator, Memento, Interpreter, Visitor, Template Method, Chain of Responsibility, Iterator.

🚀 Modern / New Design Patterns (Beyond GoF)

Today’s software systems (Cloud, Microservices, Big Data, AI) need patterns beyond GoF. Here are some important ones:

1. Dependency Injection (DI)

Promotes loose coupling by injecting dependencies instead of creating them inside a class.

Widely used in .NET Core, Spring Boot, Angular.

public class OrderService
{
    private readonly IPaymentGateway _paymentGateway;
    public OrderService(IPaymentGateway paymentGateway)
 => _paymentGateway = paymentGateway;
    public void PlaceOrder() => _paymentGateway.Process();
}

2. Repository Pattern

Abstracts database access to keep business logic independent.
Used in DDD (Domain-Driven Design) and enterprise apps.

3. CQRS (Command Query Responsibility Segregation)

Separates read and write operations for better scalability.
Common in microservices + event sourcing.

4. Saga Pattern (Microservices)

Handles distributed transactions across microservices.
Uses event-driven orchestration or choreography to maintain consistency.

5. Event Sourcing

State changes are stored as events (not just final values).
Used in banking, e-commerce order history, blockchain-like systems.

6. Circuit Breaker Pattern

Prevents cascading failures by stopping requests to a failing service.
Implemented in Polly (.NET), Resilience4j (Java).

7. API Gateway Pattern

Acts as a single entry point for microservices.
Handles routing, load balancing, authentication, caching.

8. Strangler Fig Pattern

Gradually replaces legacy systems by routing new features to modern services while
old ones still run.

🔑 Conclusion

GoF Patterns are still foundational for object-oriented design.
Modern patterns are essential for cloud, distributed systems, and microservices.
By combining both, developers can build scalable, reliable, and future-proof applications.