Abstract methods in Java - Mini Project: Build & Apply

Abstract Methods in Java

📖 Scenario: Imagine you are creating a simple program for different types of vehicles. Each vehicle can start its engine, but the way it starts is different for each type.

🎯 Goal: You will create an abstract class with an abstract method, then create subclasses that provide their own version of this method. Finally, you will create objects and call the method to see the different outputs.

📋 What You'll Learn

Create an abstract class called Vehicle with an abstract method startEngine().

Create two subclasses called Car and Motorcycle that extend Vehicle.

Override the startEngine() method in both subclasses with their own messages.

Create objects of Car and Motorcycle and call their startEngine() methods.

💡 Why This Matters

🌍 Real World

Abstract classes and methods help organize code when different objects share common behavior but implement details differently, like vehicles starting engines.

💼 Career

Understanding abstract methods is important for designing flexible and reusable code in many software development jobs.

1

Create the abstract class

Create an abstract class called Vehicle with an abstract method startEngine() that returns void.

Java

abstract class Vehicle {
    // Your code here
}

Need a hint?

Use the abstract keyword before the class and method. The method has no body.

2

Create subclasses with method overrides

Create two classes called Car and Motorcycle that extend Vehicle. Override the startEngine() method in both classes to print "Car engine started" and "Motorcycle engine started" respectively.

Java

abstract class Vehicle {
    abstract void startEngine();
}

// Your code here

Need a hint?

Use extends Vehicle and add @Override before the method.

3

Create objects and call methods

In a Main class, create a main method. Inside it, create one object of Car called myCar and one object of Motorcycle called myMotorcycle. Call startEngine() on both objects.

Java

abstract class Vehicle {
    abstract void startEngine();
}

class Car extends Vehicle {
    @Override
    void startEngine() {
        System.out.println("Car engine started");
    }
}

class Motorcycle extends Vehicle {
    @Override
    void startEngine() {
        System.out.println("Motorcycle engine started");
    }
}

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

Need a hint?

Create objects with new and call the method with dot notation.

4

Run and display output

Run the program and print the output of calling startEngine() on both myCar and myMotorcycle.

Java

abstract class Vehicle {
    abstract void startEngine();
}

class Car extends Vehicle {
    @Override
    void startEngine() {
        System.out.println("Car engine started");
    }
}

class Motorcycle extends Vehicle {
    @Override
    void startEngine() {
        System.out.println("Motorcycle engine started");
    }
}

public class Main {
    public static void main(String[] args) {
        Car myCar = new Car();
        Motorcycle myMotorcycle = new Motorcycle();
        myCar.startEngine();
        myMotorcycle.startEngine();
        // Output is shown above
    }
}

Need a hint?

When you run the program, you should see two lines printed, one for each vehicle.