11. Composition vs Inheritance: 'HAS-A' vs 'IS-A'

Scenario

"Favor Composition over Inheritance" is a core design principle. This practice shows how to reuse code by having an object of another class as a field, rather than extending it.

Code Block

class Engine {
    void start() { System.out.println("Engine roaring..."); }
}

// Inheritance (Is-A) - Bad if we just want the engine's behavior
// class Car extends Engine { } 

// Composition (Has-A) - Better
class Car {
    private final Engine engine; // Composition
    
    Car(Engine engine) {
        this.engine = engine;
    }
    
    void drive() {
        engine.start();
        System.out.println("Car is moving");
    }
}

public class Main {
    public static void main(String[] args) {
        Engine e = new Engine();
        Car myCar = new Car(e);
        myCar.drive();
    }
}

Take Your Shot

Predicted Output

Type exactly what you think will be printed in the console.