Composition

// ========== Composition: Car owns Engine ==========

// Part class - cannot exist without Car
class Engine {
    private String type;
    private int horsepower;

    public Engine(String type, int horsepower) {
        this.type = type;
        this.horsepower = horsepower;
    }

    public void start() {
        System.out.println(type + " engine starting...");
    }

    public void stop() {
        System.out.println(type + " engine stopping...");
    }
}

// Whole class - creates and owns Engine
class Car {
    private String brand;
    private Engine engine;  // Composition - Car owns Engine

    public Car(String brand, String engineType, int horsepower) {
        this.brand = brand;
        // Car creates Engine - Engine's lifecycle tied to Car
        this.engine = new Engine(engineType, horsepower);
    }

    public void start() {
        System.out.println(brand + " starting...");
        engine.start();  // Delegate to part
    }

    public void stop() {
        engine.stop();
        System.out.println(brand + " stopped.");
    }
}

// Usage
public class Main {
    public static void main(String[] args) {
        Car tesla = new Car("Tesla", "Electric", 450);
        tesla.start();
        tesla.stop();
        
        tesla = null;  // Car destroyed -> Engine destroyed too
    }
}