link: OOP

Polymorphism

Overview

Polymorphism, derived from Greek words meaning “many forms,” is a fundamental concept in object-oriented programming that allows objects of different classes to be treated as objects of a common superclass. It is closely related to inheritance, as it allows classes to be related through their behaviors while retaining their own unique implementations of those behaviors.

Abstract

Polymorphism enables a single action to be processed in different ways, and it’s a key component of the Inheritance principle, which allows one class to inherit fields and methods from another.

Content

Practical Example

Consider a base class called Animal with a method named animalSound(). Various derived classes such as Pig, Cat, Dog, and Bird might implement this method to produce sounds appropriate to each type of animal:

csharp

class Animal  // Base class (parent) 
{
 public void animalSound() 
 {
   Console.WriteLine("The animal makes a sound");
 }
}
 
class Pig : Animal  // Derived class (child) 
{
 public void animalSound() 
 {
   Console.WriteLine("The pig says: wee wee");
 }
}
 
class Dog : Animal  // Derived class (child) 
{
 public void animalSound() 
 {
   Console.WriteLine("The dog says: bow wow");
 }
}
 
class Program 
{
 static void Main(string[] args) 
 {
   Animal myAnimal = new Animal();  // Create a Animal object
   Animal myPig = new Pig();  // Create a Pig object
   Animal myDog = new Dog();  // Create a Dog object
 
   myAnimal.animalSound();
   myPig.animalSound();
   myDog.animalSound();
 }
}

The output will be:

The animal makes a sound The animal makes a sound The animal makes a sound

Not The Output I Was Looking For

The output from the example above was probably not what you expected. That is because the base class method overrides the derived class method, when they share the same name.

However, C# provides an option to override the base class method, by adding the virtual keyword to the method inside the base class, and by using the override keyword for each derived class methods

csharp

class Animal  // Base class (parent) 
{
 public virtual void animalSound() 
 {
   Console.WriteLine("The animal makes a sound");
 }
}
 
class Pig : Animal  // Derived class (child) 
{
 public override void animalSound() 
 {
   Console.WriteLine("The pig says: wee wee");
 }
}
 
class Dog : Animal  // Derived class (child) 
{
 public override void animalSound() 
 {
   Console.WriteLine("The dog says: bow wow");
 }
}
 
class Program 
{
 static void Main(string[] args) 
 {
   Animal myAnimal = new Animal();  // Create a Animal object
   Animal myPig = new Pig();  // Create a Pig object
   Animal myDog = new Dog();  // Create a Dog object
 
   myAnimal.animalSound();
   myPig.animalSound();
   myDog.animalSound();
 }
} 

The output will be: The animal makes a sound The pig says: wee wee The dog says: bow wow

With this setup, each animalSound() invocation respects the object’s actual class, thanks to polymorphism.

Summary

Benefits of Using Inheritance and Polymorphism:

• Code Reusability: Leverage existing fields and methods when creating new classes.
• Flexibility: Implement shared methods differently across multiple subclasses.
• Scalability: Manage growing codebases more effectively by grouping common logic and extending it where necessary.

References

Polymorphism - w3school