Abstract vs concrete classes in Java - Hands-On Comparison

Abstract vs Concrete Classes in Java

📖 Scenario: Imagine you are creating a simple program for a zoo. Different animals have some common behaviors, but some behaviors are specific to each animal.

🎯 Goal: You will create an abstract class Animal with an abstract method and a concrete method. Then, you will create a concrete subclass Dog that implements the abstract method. Finally, you will create an object of Dog and call its methods to see the output.

📋 What You'll Learn

Create an abstract class called Animal

Add an abstract method makeSound() in Animal

Add a concrete method sleep() in Animal that prints "The animal is sleeping"

Create a concrete class called Dog that extends Animal

Implement the makeSound() method in Dog to print "Woof!"

Create an object of Dog and call both makeSound() and sleep() methods

💡 Why This Matters

🌍 Real World

Abstract classes help programmers define common features for a group of related objects, like animals in a zoo, while allowing specific details to be filled in by subclasses.

💼 Career

Understanding abstract vs concrete classes is important for designing clean, reusable code in many software development jobs, especially in object-oriented programming.

1

Create the abstract class Animal

Create an abstract class called Animal with an abstract method makeSound() and a concrete method sleep() that prints "The animal is sleeping".

Java

abstract class Animal {
    // Your code here
}

Need a hint?

Use the abstract keyword before the class and the method makeSound(). The method sleep() should have a body that prints the message.

2

Create the concrete class Dog

Create a concrete class called Dog that extends Animal and implement the abstract method makeSound() to print "Woof!".

Java

abstract class Animal {
    abstract void makeSound();

    void sleep() {
        System.out.println("The animal is sleeping");
    }
}

class Dog extends Animal {
    // Your code here
}

Need a hint?

Remember to use extends Animal and provide the body for makeSound() that prints "Woof!".

3

Create a Dog object and call methods

Create an object of class Dog named myDog and call its makeSound() and sleep() methods.

Java

abstract class Animal {
    abstract void makeSound();

    void sleep() {
        System.out.println("The animal is sleeping");
    }
}

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

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

Need a hint?

Create the object with new Dog() and call the methods using the object name myDog.

4

Run the program and see the output

Run the program and observe the output. It should print "Woof!" followed by "The animal is sleeping".

Java

abstract class Animal {
    abstract void makeSound();

    void sleep() {
        System.out.println("The animal is sleeping");
    }
}

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

public class Main {
    public static void main(String[] args) {
        Dog myDog = new Dog();
        myDog.makeSound();
        myDog.sleep();
    }
}

// Run the program to see the output

Need a hint?

Make sure you run the Main class. The output should show the dog's sound and the sleeping message.