      1  public class Car extends Vehicle

      2  {

      3     // This instance variable is added to the subclass

      4     private String licensePlateNumber;

      5

      6     public Car()

      7     {

      8        setNumberOfTires(4);

      9        licensePlateNumber = "??????";

     10     }

     11

     12     public void setLicensePlateNumber(String newValue)

     13     {

     14        licensePlateNumber = newValue;

     15     }

     16

     17     public String toString()

     18     {

     19        return super.toString() + "[licensePlateNumber=" + licensePlateNumber + "]";

     20        // This is a good way of implementing toString in a subclass--see Special Topic 9.6

     21     }

     22  }