Interface declaration in Java - Mini Project: Build & Apply

Interface declaration

📖 Scenario: You are creating a simple program to represent different types of vehicles. Each vehicle should be able to start and stop. To ensure all vehicles have these abilities, you will use an interface.

🎯 Goal: Build a Java interface called Vehicle with two methods: start() and stop(). Then create a class that implements this interface.

📋 What You'll Learn

Create an interface named Vehicle

Declare two methods in Vehicle: start() and stop()

Create a class named Car that implements the Vehicle interface

Implement the start() and stop() methods in the Car class

Print messages inside start() and stop() methods to show when they are called

💡 Why This Matters

🌍 Real World

Interfaces help programmers design clear contracts for what classes should do, like vehicles having start and stop actions.

💼 Career

Understanding interfaces is essential for Java developers to write flexible and maintainable code, especially in large projects and frameworks.

1

Create the Vehicle interface

Create an interface called Vehicle with two method declarations: void start() and void stop().

Java

// Your code here

Need a hint?

An interface only declares methods without bodies. Use void return type and no method body.

2

Create the Car class implementing Vehicle

Create a class called Car that implements the Vehicle interface.

Java

public interface Vehicle {
    void start();
    void stop();
}

// Your code here

Need a hint?

Use implements Vehicle after the class name. Add empty method bodies for now.

3

Implement start() and stop() methods

Inside the Car class, implement the start() method to print "Car started" and the stop() method to print "Car stopped".

Java

public interface Vehicle {
    void start();
    void stop();
}

public class Car implements Vehicle {
    public void start() {
        // Print "Car started" here
    }
    public void stop() {
        // Print "Car stopped" here
    }
}

Need a hint?

Use System.out.println() to print messages inside the methods.

4

Test the Car class methods

Create a Main class with a main method. Inside main, create a Car object and call its start() and stop() methods.

Java

public interface Vehicle {
    void start();
    void stop();
}

public class Car implements Vehicle {
    public void start() {
        System.out.println("Car started");
    }
    public void stop() {
        System.out.println("Car stopped");
    }
}

// Your code here

Need a hint?

Use System.out.println() to print inside start() and stop(). Then call these methods on the Car object in main.