Why polymorphism is needed in Java - See It in Action

Why Polymorphism is Needed in Java

📖 Scenario: Imagine you are building a simple program to manage different types of animals in a zoo. Each animal can make a sound, but the sound is different for each animal. You want to write code that can handle any animal without changing the main program every time you add a new animal.

🎯 Goal: Build a Java program that shows why polymorphism is needed by creating a base class and subclasses with different behaviors, then using polymorphism to call the correct behavior without changing the main code.

📋 What You'll Learn

Create a base class called Animal with a method makeSound().

Create two subclasses Dog and Cat that override makeSound() with their own sounds.

Create a list of Animal objects containing both Dog and Cat.

Use a for loop to call makeSound() on each animal in the list.

Print the sounds to show polymorphism in action.

💡 Why This Matters

🌍 Real World

Polymorphism is used in many software systems to handle different types of objects through a common interface, like different payment methods in an app or different shapes in a drawing program.

💼 Career

Understanding polymorphism is essential for Java developers to write clean, maintainable, and scalable code that can easily adapt to new requirements.

1

Create the base class Animal

Create a class called Animal with a method makeSound() that prints "Some sound".

Java

class Animal {
    void makeSound() {
        // Your code here
    }
}

Need a hint?

The makeSound() method should print a generic sound.

2

Create subclasses Dog and Cat overriding makeSound()

Create classes Dog and Cat that extend Animal. Override makeSound() in Dog to print "Woof" and in Cat to print "Meow".

Java

class Animal {
    void makeSound() {
        System.out.println("Some sound");
    }
}

// Your code here

Need a hint?

Use extends Animal to create subclasses and override makeSound() with @Override.

3

Create a list of Animal objects with Dog and Cat

Create a List<Animal> called animals and add new Dog() and Cat() objects to it.

Java

import java.util.List;
import java.util.ArrayList;

class Animal {
    void makeSound() {
        System.out.println("Some sound");
    }
}

class Dog extends Animal {
    @Override
    void makeSound() {
        System.out.println("Woof");
    }
}

class Cat extends Animal {
    @Override
    void makeSound() {
        System.out.println("Meow");
    }
}

public class Main {
    public static void main(String[] args) {
        // Your code here
    }
}

Need a hint?

Use List<Animal> and new ArrayList<>() to create the list, then add the objects.

4

Use polymorphism to call makeSound() on each animal

Use a for loop with variable animal to go through animals and call animal.makeSound(). Print the sounds to show polymorphism.

Java

import java.util.List;
import java.util.ArrayList;

class Animal {
    void makeSound() {
        System.out.println("Some sound");
    }
}

class Dog extends Animal {
    @Override
    void makeSound() {
        System.out.println("Woof");
    }
}

class Cat extends Animal {
    @Override
    void makeSound() {
        System.out.println("Meow");
    }
}

public class Main {
    public static void main(String[] args) {
        List animals = new ArrayList();
        animals.add(new Dog());
        animals.add(new Cat());

        // Your code here
    }
}

Need a hint?

Use a for loop with Animal animal : animals and call animal.makeSound().