5.7 Polymorphism

Let’s go through polymorphism in C# — another core concept of object-oriented programming (OOP).

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📌 1. What is Polymorphism?

Polymorphism means “many forms”. In C#, it allows a single interface or method to have different behaviors depending on the object or context.

• Enables flexible and reusable code

• Often works together with inheritance

• Two main types in C#:

  1. Compile-time (Static) Polymorphism

  2. Run-time (Dynamic) Polymorphism

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📌 2. Compile-Time Polymorphism (Method Overloading)

• Same method name with different parameters

• Determined at compile time

public class Calculator
{
    public int Add(int a, int b) => a + b;
    public double Add(double a, double b) => a + b;
    public int Add(int a, int b, int c) => a + b + c;
}
 
// Usage
Calculator calc = new Calculator();
Console.WriteLine(calc.Add(2, 3));      // 5
Console.WriteLine(calc.Add(2.5, 3.5));  // 6
Console.WriteLine(calc.Add(1, 2, 3));   // 6

• Same method name, different parameters → compiler decides which one to call

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📌 3. Run-Time Polymorphism (Method Overriding)

• Method behavior is determined at runtime

• Uses inheritance + virtual/override keywords

public class Animal
{
    public virtual void MakeSound()
    {
        Console.WriteLine("Some generic sound");
    }
}
 
public class Dog : Animal
{
    public override void MakeSound()
    {
        Console.WriteLine("Bark!");
    }
}
 
public class Cat : Animal
{
    public override void MakeSound()
    {
        Console.WriteLine("Meow!");
    }
}
 
// Usage
Animal a1 = new Dog();
Animal a2 = new Cat();
 
a1.MakeSound(); // Bark!
a2.MakeSound(); // Meow!

• Same method (MakeSound) behaves differently depending on the object type

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📌 4. Key Keywords

Keyword	Use
virtual	Base class method can be overridden
override	Derived class method overrides base class
new	Hides base class method (not true polymorphism)

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📌 5. Polymorphism Benefits

1. Code Reusability → Same method name for different behaviors

2. Flexibility → Works with different types of objects

3. Maintainability → Can add new derived classes without changing existing code

4. Simplifies API → Users don’t need to know exact class type

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📌 6. Summary Table

Type	How Achieved	Example
Compile-Time (Static)	Method Overloading	Add(int,int) vs Add(double,double)
Run-Time (Dynamic)	Method Overriding	virtual + override
Key Concept	Same name, different behavior	MakeSound() behaves differently for Dog/Cat

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✅ Tip:

• Use compile-time polymorphism for convenience and readability

• Use run-time polymorphism to leverage inheritance and allow objects to behave differently dynamically