Implement a singleton class
💡 Concept: Singleton Design Pattern
The singleton pattern restricts a class to a single instance, ensuring controlled access and lazy initialization.
📘 Quick Intro
Singleton ensures only one object is created and provides a global access point.
🧠 Analogy
Like a president managing a country, only one can hold the office at a time.
🔧 Technical Explanation
- Private constructor prevents instantiation outside the class.
- Static instance holds the single created object.
- Thread safety achieved with locks or static initialization.
- Lazy initialization delays instance creation until first use.
- Ensures resource optimization and consistent state.
🎯 Use Cases
- ✅ Logging frameworks.
- ✅ Configuration managers.
- ✅ Database connection pools.
- ✅ Caching mechanisms.
💻 Code Example
// Thread-safe singleton implementation
public sealed class Singleton {
private static readonly Lazy<Singleton> instance = new Lazy<Singleton>(() => new Singleton());
public static Singleton Instance => instance.Value;
private Singleton() {
// Private constructor
}
public void DoAction() {
Console.WriteLine(""Singleton instance action."");
}
}
❓ Interview Q&A
Q1: What is a singleton pattern?
A: Restricts class to one instance.
Q2: Why use singleton?
A: Controlled access to resources.
Q3: How to ensure thread safety?
A: Use locks or Lazy<T>.
Q4: Can you inherit singleton?
A: Generally no, use sealed class.
Q5: When is lazy initialization useful?
A: To delay resource usage.
Q6: What problems does singleton solve?
A: Multiple instance conflicts.
Q7: Is singleton a design pattern?
A: Yes, a creational pattern.
Q8: Can singleton be broken?
A: With reflection or serialization.
Q9: Alternatives to singleton?
A: Dependency injection.
Q10: Is singleton thread-safe by default?
A: Not always, must implement safety.
📝 MCQs
Q1. What does singleton ensure?
- Multiple instances
- Single instance
- No instance
- Depends on usage
Q2. How to make singleton thread-safe?
- Use locks or Lazy<T>
- Ignore thread safety
- Create multiple instances
- Use static methods
Q3. Can singleton class be inherited?
- Yes
- No
- Sometimes
- Always
Q4. What is lazy initialization?
- Immediate creation
- Delay creation
- Random creation
- No creation
Q5. Why use singleton?
- Speed
- Resource control
- Memory leaks
- Testing
Q6. Is singleton a design pattern?
- No
- Yes
- Maybe
- Rarely
Q7. What can break singleton?
- Locks
- Reflection and serialization
- Threading
- Inheritance
Q8. Alternatives to singleton?
- Singleton
- Dependency injection
- Factory pattern
- Strategy pattern
Q9. Is singleton thread-safe by default?
- Yes
- No
- Depends
- Always
Q10. When is lazy initialization useful?
- Never
- Always
- Delay resource usage
- Immediately
💡 Bonus Insight
The singleton pattern is essential for resource management and global state consistency.
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