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Static Class: A static class in C# is used to group utility functions or methods that don’t require an instance of the class. Static classes cannot be instantiated, and all members of the class are static.
Singleton Pattern: A singleton ensures that only one instance of a class is created, providing a global point of access to the instance. Singleton classes can maintain instance state and are flexible with instantiation.
Key Differences: Static Class vs Singleton Pattern
| Aspect | Static Class | Singleton Pattern |
|---|---|---|
| Instantiation | Cannot be instantiated | Single instance created lazily or eagerly |
| State | No instance state | Maintains instance-specific state |
| Constructor | No constructor | Private constructor to control instantiation |
| Thread Safety | Explicit synchronization needed | Managed internally (lock or thread-safe singleton) |
| Use Case | Utility or helper functions | Managing shared resources (e.g., database connections) |
When to Use Each
- Static Class: Use a static class for grouping utility methods that do not require instance-specific data.
- Singleton Pattern: Use the singleton pattern when you need to manage state and ensure only one instance of a class is used (e.g., a logging service or database connection).
Interview Questions
1. Can a Singleton be implemented without locking for thread safety?
Answer: Yes, you can implement a thread-safe singleton using the Lazy<T> class in C#, which handles thread safety internally.
2. Why use a singleton over a static class for a logger?
Answer: A singleton allows for better flexibility and can maintain state (like logging configurations), while a static class would not have this flexibility.
3. Can a singleton be garbage collected?
Answer: Yes, a singleton can be garbage collected if no references to the instance are being held and it is no longer used.
4. Can static methods be called on a singleton class?
Answer: Yes, a singleton class can have static methods that are called without instantiating the class. However, the main idea of a singleton is to have a single instance, so instance methods are typically used.
5. What is the difference between a non-static class, a static class, and a singleton?
Answer:
- Non-Static Class: Can be instantiated multiple times, each instance having its own state.
- Static Class: Cannot be instantiated; used for utility methods. All members are static and shared across the application.
- Singleton Class: Ensures a single instance of the class exists, maintaining state across the application.
Complete Analysis of Static, Singleton, and Non-Static Classes
Static Class: Use static classes for methods that do not require instance-level data and are meant to be shared. Static classes cannot be inherited or instantiated and are typically used for utility functions like logging, math operations, or configuration methods.
Singleton Class: The singleton pattern is useful when you need exactly one instance of a class throughout the application, especially when managing shared resources like database connections or caching mechanisms. Singleton ensures that any class that depends on the resource can access the same instance, maintaining a consistent state.
Non-Static Class: This is the standard approach in object-oriented programming. Non-static classes can be instantiated multiple times, with each instance having its own state. This is useful when multiple, independent copies of the class are needed.
More Interview Questions on Singleton
- What are the different ways to implement a Singleton in C#?
- How can you implement a thread-safe Singleton without using locks?
- Can Singleton be inherited? If yes, how would you manage the instance in the child class?
