Object-Oriented Programming: Polymorphism and Interfaces - Java: How to Program Early Objects - page 413

10.5.5 Indirect Concrete Subclass BasePlusCommissionEmployee
Class BasePlusCommissionEmployee (Fig. 10.8) extends class CommissionEmployee (line
4) and therefore is an indirect subclass of class Employee . Class BasePlusCommission-
Employee has a constructor (lines 9-20) that receives a first name, a last name, a social se-
curity number, a sales amount, a commission rate and a base salary. It then passes all of
these except the base salary to the CommissionEmployee constructor (lines 13-14) to ini-
tialize the superclass instance variables. BasePlusCommissionEmployee also contains a set
method (lines 23-29) to assign a new value to instance variable baseSalary and a get
method (lines 32-35) to return baseSalary 's value. Method earnings (lines 38-42) cal-
culates a BasePlusCommissionEmployee 's earnings. Line 41 in method earnings calls su-
perclass CommissionEmployee 's earnings method to calculate the commission-based
portion of the employee's earnings—this is another nice example of code reuse . Base-
PlusCommissionEmployee 's toString method (lines 45-51) creates a String representa-
tion of a BasePlusCommissionEmployee that contains "base-salaried" , followed by the
String obtained by invoking superclass CommissionEmployee 's toString method (line
49), then the base salary. The result is a String beginning with "base-salaried commis-
sion employee" followed by the rest of the BasePlusCommissionEmployee 's information.
Recall that CommissionEmployee 's toString obtains the employee's first name, last name
and social security number by invoking the toString method of its superclass (i.e., Employ-
ee )—yet another example of code reuse . BasePlusCommissionEmployee 's toString initi-
ates a chain of method calls that span all three levels of the Employee hierarchy.

1 // Fig. 10.8: BasePlusCommissionEmployee.java

2 // BasePlusCommissionEmployee class extends CommissionEmployee.

3
4 public class BasePlusCommissionEmployee extends CommissionEmployee

5 {

6 private double baseSalary; // base salary per week

7
8 // constructor

9 public BasePlusCommissionEmployee(String firstName, String lastName,

10 String socialSecurityNumber, double grossSales,

11 double commissionRate, double baseSalary)

12 {

13 super (firstName, lastName, socialSecurityNumber,

14 grossSales, commissionRate);

15
16 if (baseSalary < 0.0 ) // validate baseSalary

17 throw new IllegalArgumentException( "Base salary must be >= 0.0" );

18

19 this .baseSalary = baseSalary;

20 }

21
22 // set base salary

23 public void setBaseSalary( double baseSalary)

24 {

25 if (baseSalary < 0.0 ) // validate baseSalary

26 throw new IllegalArgumentException( "Base salary must be >= 0.0" );

Fig. 10.8 | BasePlusCommissionEmployee class extends CommissionEmployee . (Part 1 of 2.)