Runtime polymorphism in Java - Mini Project: Build & Apply

Runtime Polymorphism in Java

📖 Scenario: Imagine you are creating a simple program for a zoo. Different animals make different sounds. You want to write code that can handle any animal and make it produce its sound correctly.

🎯 Goal: Build a Java program that demonstrates runtime polymorphism by using a base class Animal and subclasses Dog and Cat. The program will call the makeSound() method on different animal objects and show the correct sound for each.

📋 What You'll Learn

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

Create subclasses Dog and Cat that override makeSound().

Create an array of Animal references holding Dog and Cat objects.

Use a loop to call makeSound() on each animal and print the result.

💡 Why This Matters

🌍 Real World

Runtime polymorphism lets programs handle different objects in a flexible way, like animals making sounds without knowing their exact type beforehand.

💼 Career

Understanding runtime polymorphism is essential for Java developers to write clean, reusable, and maintainable code using inheritance and method overriding.

1

Create the base class Animal

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

Java

# Your code here

Need a hint?

Define a class named Animal. Inside it, write a method makeSound() that prints the generic sound.

2

Create subclasses Dog and Cat overriding makeSound()

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

Java

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

# Your code here

Need a hint?

Use extends Animal to create subclasses. Use @Override and redefine makeSound() to print the correct sounds.

3

Create an array of Animal references holding Dog and Cat objects

Create a public class Main with a main method. Inside main, create an array of Animal called animals that holds one Dog object and one Cat object.

Java

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

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

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

# Your code here

Need a hint?

Define a Main class with a main method. Create an array of type Animal and put new Dog() and Cat() objects inside.

4

Use a loop to call makeSound() on each animal and print the result

Inside the main method, use a for loop with variable animal to iterate over the animals array. Call animal.makeSound() inside the loop to print each animal's sound.

Java

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

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

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

public class Main {
    public static void main(String[] args) {
        Animal[] animals = {new Dog(), new Cat()};
        // Your code here
    }
}

Need a hint?

Use a for-each loop to go through each animal in the animals array. Call animal.makeSound() inside the loop to print the sounds.