Upcasting and downcasting in Java - Mini Project: Build & Apply

Upcasting and Downcasting in Java

📖 Scenario: Imagine you are creating a simple program to manage different types of animals in a zoo. Each animal can make a sound, but some animals have special sounds. You will learn how to use upcasting and downcasting to work with these animals.

🎯 Goal: Build a Java program that demonstrates upcasting and downcasting with a base class Animal and a subclass Dog. You will create objects, cast them, and call their methods to see how casting works.

📋 What You'll Learn

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

Create a subclass called Dog that extends Animal and overrides makeSound() to print "Bark".

Create an Animal reference that points to a Dog object (upcasting).

Downcast the Animal reference back to a Dog reference and call a bark() method unique to Dog.

Print outputs to show the effects of upcasting and downcasting.

💡 Why This Matters

🌍 Real World

Upcasting and downcasting are used in real-world programs to write flexible code that can work with general types but still access specific features when needed.

💼 Career

Understanding casting is important for Java developers working with inheritance, polymorphism, and designing clean, reusable code.

1

Create the base class Animal and subclass Dog

Create a class called Animal with a method makeSound() that prints "Some sound". Then create a subclass called Dog that extends Animal and overrides makeSound() to print "Bark".

Java

// Your code here

Need a hint?

Use class keyword to create classes. Use extends to make Dog a subclass of Animal. Override makeSound() in Dog.

2

Add a unique method bark() to Dog

Inside the Dog class, add a method called bark() that prints "Dog is barking".

Java

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

class Dog extends Animal {
    @Override
    void makeSound() {
        System.out.println("Bark");
    }
    // Your code here
}

Need a hint?

Define a new method bark() inside Dog that prints the message.

3

Create an Animal reference pointing to a Dog object (upcasting)

Create a variable called animal of type Animal and assign it a new Dog() object (this is upcasting). Then call animal.makeSound().

Java

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

class Dog extends Animal {
    @Override
    void makeSound() {
        System.out.println("Bark");
    }
    void bark() {
        System.out.println("Dog is barking");
    }
}

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

Need a hint?

Use Animal animal = new Dog(); to upcast. Then call animal.makeSound();.

4

Downcast the Animal reference to Dog and call bark()

Downcast the animal variable to a Dog type and store it in a variable called dog. Then call dog.bark() to print "Dog is barking".

Java

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

class Dog extends Animal {
    @Override
    void makeSound() {
        System.out.println("Bark");
    }
    void bark() {
        System.out.println("Dog is barking");
    }
}

public class Main {
    public static void main(String[] args) {
        Animal animal = new Dog();
        animal.makeSound();
        // Your code here
    }
}

Need a hint?

Use Dog dog = (Dog) animal; to downcast. Then call dog.bark();.