Can a Class Implement Multiple Interfaces in C#?
💡 Concept: Multiple Interface Implementation
Yes, a class in C# can implement multiple interfaces. This allows a class to inherit multiple behaviors without the limitations of single class inheritance.
📘 Quick Intro
Multiple interface implementation is a core concept in C# object-oriented design. While a class can only inherit from one base class, it can implement several interfaces—each defining a separate contract the class must fulfill.
🧠 Analogy
Imagine a person who is both a doctor and a writer. They follow the rules of the medical profession and writing guidelines. Similarly, a C# class can implement multiple interfaces, adhering to multiple role contracts.
🔧 Technical Explanation
- Use a comma-separated list of interface names after the class declaration.
- All members from all interfaces must be implemented unless the class is abstract.
- Explicit interface implementation can help resolve method name conflicts.
- Each interface acts as a distinct contract; the class promises to provide implementations.
- This feature supports multiple inheritance-like behavior in C#.
🎯 Use Cases
- When a class needs to serve multiple roles (e.g.,
ILoggerandIFormatter). - Building scalable and testable applications with dependency injection.
- Unit testing via mockable interfaces.
- Composing functionality without inheritance conflicts.
💻 Real Code Example
public interface IReadable {
void Read();
}
public interface IWritable {
void Write();
}
public class Document : IReadable, IWritable {
public void Read() {
Console.WriteLine(""Reading document..."");
}
public void Write() {
Console.WriteLine(""Writing document..."");
}
}
❓ Interview Q&A
Q1: Can a class implement multiple interfaces?
A: Yes, it can implement any number of interfaces.
Q2: Why use multiple interfaces in a class?
A: To separate concerns and increase flexibility.
Q3: What happens if two interfaces have methods with the same name?
A: Use explicit implementation to resolve conflicts.
Q4: Can an interface extend multiple interfaces?
A: Yes, interfaces can inherit from multiple interfaces.
Q5: Does multiple interface implementation cause ambiguity?
A: Not if managed with proper method resolution.
Q6: Is multiple interface implementation runtime polymorphism?
A: Yes, it's a form of interface-based polymorphism.
Q7: Can interfaces contain fields?
A: No, interfaces only declare members.
Q8: Can interfaces define static methods?
A: Yes, starting from C# 8.
Q9: Is interface implementation required to be public?
A: Yes, unless explicitly implemented.
Q10: Can a struct implement interfaces?
A: Yes, structs can implement interfaces.
📝 MCQs
Q1. What does a class use to implement multiple interfaces?
- Inheritance
- Generic types
- Comma-separated list
- Partial classes
Q2. Can a class inherit multiple interfaces in C#?
- No
- Yes
- Only one
- Only abstract interfaces
Q3. What is a benefit of implementing multiple interfaces?
- More memory use
- Faster compilation
- Separation of concerns
- Single responsibility
Q4. What feature allows different behaviors with same method name?
- Overloading
- Inheritance
- Explicit implementation
- Casting
Q5. Which type cannot implement multiple interfaces?
- Class
- Struct
- Record
- All can
Q6. Are method conflicts possible with multiple interfaces?
- No
- Yes
- Only with generics
- If sealed
Q7. Can interfaces be inherited by other interfaces?
- No
- Yes
- Only one
- Only internal ones
Q8. Which version introduced static members in interfaces?
- C# 6
- C# 7
- C# 8
- C# 9
Q9. How does C# handle interface member implementation?
- Optional
- Only override
- Class must define all members
- None of these
Q10. What keyword is used to implement interfaces?
- ::
- implements
- : (colon)
- new
💡 Bonus Insight
Interfaces allow combining roles from different domains. This composition-based design is at the heart of clean, testable software in C# applications.
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