d2_aggregation

public class Teacher {
    private String name;
    public void teach(){

    }
}

public class University {
    private List<Teacher> teacherList;
}

public class Car {
    private Engine engine;
    private Tyre tyre;

    public Car() {
       engine = new Engine();
       tyre = new Tyre();
    }
}

public class Car {
    private Engine engine;
    private List<Tyre> tyres;

    // 构造方法
    public Car(Engine engine, List<Tyre> tyres) {
        this.engine = engine;
        this.tyres = tyres;
    }

    // drive方法
    public void drive() {
        // 检查引擎和轮胎状态
        if (engine == null) {
            System.out.println("Cannot drive: No engine installed!");
            return;
        }

        if (tyres == null || tyres.size() != 4) {
            System.out.println("Cannot drive: Need exactly 4 tyres!");
            return;
        }

        // 启动过程
        System.out.println("Starting engine...");
        System.out.println("Engine running at " + engine.getHorsepower() + " horsepower");

        // 检查轮胎
        System.out.println("Checking tyres...");
        for (int i = 0; i < tyres.size(); i++) {
            Tyre tyre = tyres.get(i);
            System.out.println("Tyre " + (i+1) + ": " + tyre.getBrand() + " brand");
        }

        // 开始行驶
        System.out.println("Car is now driving smoothly!");
    }

    // Getter和Setter方法保持不变
    public Engine getEngine() {
        return engine;
    }

    public void setEngine(Engine engine) {
        this.engine = engine;
    }

    public List<Tyre> getTyres() {
        return tyres;
    }

    public void setTyres(List<Tyre> tyres) {
        this.tyres = tyres;
    }
}

public class Engine {
    private int horsepower;

    public int getHorsepower() {
        return horsepower;
    }

    public void setHorsepower(int horsepower) {
        this.horsepower = horsepower;
    }
}

public class Tyre {
    private String brand;

    public String getBrand() {
        return brand;
    }

    public void setBrand(String brand) {
        this.brand = brand;
    }
}