Polymorphism

C# Polymorphism

Polymorphism in C# refers to the ability of objects to take on different forms. It allows methods to behave differently based on the object that calls them, enabling flexibility and reusability in code.

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Key Concepts of Polymorphism

1. Compile-Time Polymorphism (Static Polymorphism)

   • Achieved through method overloading and operator overloading.
   • The behavior is determined at compile time.

2. Run-Time Polymorphism (Dynamic Polymorphism)

   • Achieved through method overriding using inheritance.
   • The behavior is determined at runtime.

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1. Compile-Time Polymorphism (Method Overloading)

Definition:

• Method overloading allows multiple methods with the same name but different parameters in the same class.

Example:

class Calculator {
    public int Add(int a, int b) {
        return a + b;
    }

    public double Add(double a, double b) {
        return a + b;
    }

    public int Add(int a, int b, int c) {
        return a + b + c;
    }
}

// Usage
Calculator calc = new Calculator();
Console.WriteLine(calc.Add(5, 3));       // Output: 8
Console.WriteLine(calc.Add(5.5, 3.3));   // Output: 8.8
Console.WriteLine(calc.Add(1, 2, 3));    // Output: 6

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2. Run-Time Polymorphism (Method Overriding)

Definition:

• A derived class overrides a base class method using the virtual and override keywords.

Example:

class Animal {
    public virtual void Speak() {
        Console.WriteLine("The animal makes a sound.");
    }
}

class Dog : Animal {
    public override void Speak() {
        Console.WriteLine("The dog barks.");
    }
}

class Cat : Animal {
    public override void Speak() {
        Console.WriteLine("The cat meows.");
    }
}

// Usage
Animal animal1 = new Dog();
animal1.Speak(); // Output: The dog barks.

Animal animal2 = new Cat();
animal2.Speak(); // Output: The cat meows.

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Polymorphism with Interfaces

• Interfaces provide polymorphism by ensuring a class implements certain methods.

Example:

interface IShape {
    void Draw();
}

class Circle : IShape {
    public void Draw() {
        Console.WriteLine("Drawing a circle.");
    }
}

class Rectangle : IShape {
    public void Draw() {
        Console.WriteLine("Drawing a rectangle.");
    }
}

// Usage
IShape shape1 = new Circle();
shape1.Draw(); // Output: Drawing a circle.

IShape shape2 = new Rectangle();
shape2.Draw(); // Output: Drawing a rectangle.

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Key Terms

Term	Description
Method Overloading	Multiple methods with the same name but different signatures.
Method Overriding	Redefining a method in a derived class to change its behavior.
Virtual	Indicates that a method can be overridden in a derived class.
Override	Used in the derived class to override a virtual method.
Abstract	Defines a method without implementation in a base class, requiring derived classes to implement it.
Interface	Provides a contract for classes to implement methods, enabling polymorphism.

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Differences Between Overloading and Overriding

Aspect	Overloading	Overriding
Definition	Same method name, different parameters.	Redefining a method in the derived class.
Polymorphism Type	Compile-time	Run-time
Keyword	No special keywords.	virtual, override, abstract
Class Relationship	Same class.	Requires inheritance.

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Example Combining Overloading and Overriding

Example:

class BaseClass {
    public virtual void Display(string message) {
        Console.WriteLine("Base class message: " + message);
    }
}

class DerivedClass : BaseClass {
    public override void Display(string message) {
        Console.WriteLine("Derived class message: " + message);
    }

    // Overloading
    public void Display(string message, int count) {
        for (int i = 0; i < count; i++) {
            Console.WriteLine(message);
        }
    }
}

// Usage
BaseClass baseObj = new BaseClass();
baseObj.Display("Hello from Base!"); // Output: Base class message: Hello from Base!

DerivedClass derivedObj = new DerivedClass();
derivedObj.Display("Hello from Derived!");       // Output: Derived class message: Hello from Derived!
derivedObj.Display("Hello again!", 3);           // Output: Hello again! (3 times)

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Summary

• Polymorphism provides flexibility by allowing a single interface to represent different types of behavior.
• Types:
  • Compile-Time: Method overloading and operator overloading.
  • Run-Time: Method overriding using inheritance.
• Use polymorphism to enhance code reusability, maintainability, and extensibility.

Polymorphism is a cornerstone of object-oriented programming, ensuring better design and reduced redundancy.