May 19th, 2013 at 12:51 AM

Polymorphism and Overriding Methods

Lecture Inheritance lets us inherit fields and methods from another class. Polymorphism uses those methods to perform different tasks. This allows us to perform a single action in different ways. Code Example

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");
  }
}

NB: if you don't use virtual and override keywords the output will not be changed: The animal makes a sound The animal makes a sound The animal makes a sound The above code must to rewrite to the following:

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