What is Polymorphism in C#?
💡 Concept: Polymorphism in C#
Polymorphism is a core concept in object-oriented programming that allows objects to be treated as instances of their parent class, while invoking the overridden or overloaded behavior at runtime or compile time respectively.
📘 Quick Intro
In C#, polymorphism enables code flexibility and extensibility. There are two main types: compile-time (method overloading) and run-time (method overriding via inheritance).
🧠 Analogy
Think of a remote control. Regardless of whether it controls a TV, AC, or speaker, pressing the "Power" button performs the appropriate action. Polymorphism is like that — the same interface triggers different results depending on the object.
🔧 Technical Explanation
- 🔁 Compile-time polymorphism uses method overloading (same method name, different parameters).
- 🧩 Run-time polymorphism is achieved by using
virtualandoverridekeywords with inheritance. - 🧠 Base class references can call overridden methods in derived classes using dynamic dispatch.
- ⚠️ Polymorphism requires the use of inheritance or interfaces for run-time flexibility.
🎯 Use Cases
- 📦 Designing APIs and libraries that work with general types but allow specific behavior.
- ♻️ Replacing long
if-elseorswitchconditions with object behavior. - 📈 Making systems more extensible and easier to maintain.
💻 Real Code Example
// Compile-time Polymorphism (Overloading)
public class Calculator {
public int Add(int a, int b) => a + b;
public double Add(double a, double b) => a + b;
}
// Run-time Polymorphism (Overriding)
public class Animal {
public virtual void Speak() => Console.WriteLine("Animal speaks");
}
public class Dog : Animal {
public override void Speak() => Console.WriteLine("Dog barks");
}
Animal pet = new Dog();
pet.Speak(); // Outputs: Dog barks
❓ Interview Q&A
Q1: What is polymorphism in C#?
A: It allows methods to behave differently based on the object context.
Q2: What is compile-time polymorphism?
A: It's method overloading resolved during compilation.
Q3: What is run-time polymorphism?
A: It’s method overriding resolved during program execution.
Q4: What keyword enables overriding in C#?
A: virtual in base and override in derived class.
Q5: Can constructors be overloaded?
A: Yes, constructors support overloading.
Q6: What is method hiding?
A: It occurs when a derived class defines a method with the same name and uses the new keyword.
Q7: Is method overloading polymorphism?
A: Yes, it is compile-time polymorphism.
Q8: Can private methods be overridden?
A: No, only accessible and virtual methods can be overridden.
Q9: Why use polymorphism?
A: To enable extensibility and code reuse.
Q10: Can interfaces support polymorphism?
A: Yes, interfaces enable polymorphism by allowing different implementations.
📝 MCQs
Q1. What is compile-time polymorphism?
- Method overriding
- Method hiding
- Method overloading
- Inheritance
Q2. Which keyword enables runtime polymorphism?
- const
- new
- override
- virtual
Q3. What is the result of method overriding?
- Compile error
- Static dispatch
- Dynamic behavior at runtime
- Interface implementation
Q4. Which is NOT a form of polymorphism?
- Method overloading
- Method overriding
- Method serialization
- Virtual dispatch
Q5. Which access modifier is needed for polymorphism?
- private
- sealed
- public/protected
- internal
Q6. Which C# keyword hides a base method?
- static
- base
- new
- override
Q7. Which method call supports late binding?
- Overloaded method
- Static method
- Overridden method
- Sealed method
Q8. What’s the advantage of polymorphism?
- Shorter code
- Less memory
- Faster runtime
- Flexibility and extensibility
Q9. Can polymorphism be achieved via interfaces?
- No
- Yes
- Only with abstract classes
- Only in Java
Q10. What is dynamic dispatch?
- Call to dynamic keyword
- Method call determined at compile time
- Method call determined at runtime
- Compiler optimization
💡 Bonus Insight
Polymorphism makes your code flexible and future-proof. By programming to interfaces or base types, you allow extensions without modifying existing logic — a key principle of the Open/Closed principle in SOLID design.
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