java polymorphism

Java Polymorphism

Polymorphism means "many forms", and it occurs when we have many classes that are related to each other by inheritance.

Like we specified in the previous chapter;

Inheritance lets us

inherit attributes and methods from another class. Polymorphism

uses those methods to perform different tasks. This allows us to perform a single

action in different ways.

For example, think of a superclass called Animal that has a method called animalSound(). Subclasses of Animals could be Pigs, Cats, Dogs, Birds - And they also have their own implementation of an animal sound (the pig oinks, and the cat meows, etc.):

Example

class Animal {

  public void animalSound() {

    System.out.println("The animal makes a sound");

  }

}



class Pig extends Animal {

  public void animalSound() {

    System.out.println("The pig says: wee wee");

  }

}



class Dog extends Animal {

  public void animalSound() {

    System.out.println("The dog says: bow wow");

  }

}

Remember from the Inheritance chapter that we use the extends keyword to inherit from a class.

Now we can create Pig and

Dog objects and call the animalSound() method on both of them:

Example

class Animal {

  public void animalSound() {

    System.out.println("The animal makes a sound");

  }

}



class Pig extends Animal {

  public void animalSound() {

    System.out.println("The pig says: wee wee");

  }

}



class Dog extends Animal {

  public void animalSound() {

    System.out.println("The dog says: bow wow");

  }

}



class Main {

  public 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();

  }

}

Try it Yourself »

Why And When To Use "Inheritance" and "Polymorphism"?

- It is useful for code reusability: reuse attributes and methods of an existing class when you create a new class.