Inheritance - Absolute Java - page 443

Self-Test Exercises
1. Suppose the class named DiscountSale is a derived class of a class called Sale .
Suppose the class Sale has instance variables named price and numberOfItems .
Will an object of the class DiscountSale also have instance variables named
price and numberOfItems ?
2. Suppose the class named DiscountSale is a derived class of a class called Sale ,
and suppose the class Sale has public methods named getTotal and getTax .
Will an object of the class DiscountSale have methods named getTotal and
getTax ? If so, do these methods have to perform the exact same actions in the
class DiscountSale as in the class Sale ?
3. Suppose the class named DiscountSale is a derived class of a class called Sale ,
and suppose the class Sale has a method with the following heading and no
other methods named getTax , as follows:
public double getTax()
And suppose the defi nition of the class DiscountSale has a method defi nition
with the following heading and no other method defi nitions for methods named
getTax , as follows:
public double getTax( double rate)
How many methods named getTax will the class DiscountSale have and what
are their headings?
4. The class HourlyEmployee ( Display 7.3 ) has methods named getName and
getRate (among others). Why does the defi nition of the class HourlyEmployee
contain a defi nition of the method getRate but no defi nition of the method
getName ?
There are some restrictions on how you can use the base class constructor call
super . You cannot use an instance variable as an argument to super . Also, the call to
the base class constructor ( super ) must always be the first action taken in a constructor
definition. You cannot use it later in the definition of a constructor.
Notice that you use the keyword super to call the constructor of the base class. You
do not use the name of the constructor; you do not use
Employee(theName, theDate); //ILLEGAL
If a constructor definition for a derived class does not include an invocation of
a constructor for the base class, then the no-argument constructor of the base class
is invoked automatically as the first action of the derived class constructor. So, the