Inheritance - Absolute Java - page 463

PITFALL: You Cannot Use Multiple super s

As we already noted, within the definition of a method of a derived class, you can call
an overridden method of the base class by prefacing the method name with super
and a dot. However, you cannot repeat the use of super to invoke a method from
some ancestor class other than a direct parent. For example, suppose that the class
Employee were derived from the class Person , and the class HourlyEmployee is
derived from the class Employee . You might think that you can invoke a method of
the class Person within the definition of the class HourlyEmployee , by using super.
super , as in

super . super .toString() //ILLEGAL!

However, as the comment indicates, it is illegal to have such multiple super s in Java. ■

Self-Test Exercises

14. Redefi ne the toString method of the class SalariedEmployee ( Display 7.5 )
so that it uses super.toString() . This new defi nition of toString will be
equivalent to the one given in Display 7.5.
15. Redefi ne the equals method for the class HourlyEmployee ( Display 7.3 ) using
super.equals to invoke the equals method of the base class Employee .
16. Is the following program legal? The relevant classes are defi ned in Displays 7.2
and 7.3 .

public class EmployeeDemo
{

public static void main(String[] args)
{
HourlyEmployee joe =
new HourlyEmployee("Joe Young",
new Date("Feb", 1, 2004), 10.50, 40);
String nameNDate = joe. super .toString();
System.out.println(nameNDate);
}
}

(continued)