如何将子类构造函数解析为对象

Question

我正在编写一个程序，用于输出有关车辆信息的任务，其中Vehicle是Superclass，Car，Truck和Van是Subclasses。我们的讲师给了我们主要方法，所以我知道问题必须出在我为子类编写的代码中。

我已根据建议的反馈更新了我的代码，并在第3行遇到了新错误：无法访问AssignmentEX2类型的封闭实例。必须使用封闭的类型实例限定分配  AssignmentEX2（例如x.new A（），其中x是AssignmentEX2的实例）。

public class AssignmentEX2 {

public static void main(String[] args) {
     Vehicle vehicle = new Vehicle("5554EAWV3898");
     System.out.println(vehicle.toString());
     vehicle.rentVehicle();
     System.out.println(vehicle.toString());
     vehicle.returnVehicle();
     System.out.println(vehicle.toString());
     System.out.println();

     Car car = new Car("6903NMME5853", 4);
     System.out.println(car.toString());
     car.rentVehicle();
     System.out.println(car.toString());
     System.out.println();

     Truck truck = new Truck("7242OAHT0021", 26, 3);
     System.out.println(truck.toString());
     truck.rentVehicle();
     System.out.println(truck.toString());
     System.out.println();

     Van van = new Van("5397NQRO4899", 11);
     System.out.println(van.toString());
     van.rentVehicle();
     System.out.println(van.toString());
    } 

class Vehicle {
    String vin;
    Boolean rented = false;

public Vehicle(String vin) {
}

public String getVin() {
    return vin;
}

public Boolean isRented() {
    return rented;
}

public void rentVehicle() {
    rented = true;
}

public void returnVehicle() {
    rented = false;
}

public String toString() {
    return("VIN: " + vin + "\nRented: " + rented );
}
}

class Car extends Vehicle {
    int doors;

    public Car (String vin, int doors) {
        super( vin );
    }

    public int getDoors() {
        return doors;
    }

    public String toString() {
        return("VIN: " + vin + "\nRented: " + rented + "\nDoors: " + doors);
    }

}

class Truck extends Vehicle {
    int boxSize;
    int axles;

    public Truck(String vin, int boxSize, int axles) {
        super( vin );
    }

    public int getBoxSize() {
        return boxSize;
    }

    public int getAxles() {
        return axles;
    }

    public String toString() {
        return("VIN: " + vin + "\nRented: " + rented + "\nBox Size: " + boxSize + "\nAxles: "
                + axles);
    }
}

class Van extends Vehicle {
    int seats;

    public Van (String vin, int seats) {
        super( vin );
    }

    public int getSeats() {
        return seats;
    }

    public String toString() {
        return("VIN: " + vin + "\nRented: " + rented + "\nSeats: " + seats);
    }
}

}