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  }