Java How to Program, Early Objects, 11th Edition

... relationship between subclasses and superclasses (i.e., the is-a relationship) by assigning a subclass reference to a superclass variable. This program uses classes CommissionEmployee and BasePlusCommissionEmployee from Fig. 9.10 and Fig. 9.11, respectively.

Fig. 10.1

 1  // Fig. 10.1: PolymorphismTest.java
 2  // Assigning superclass and subclass references to superclass and
 3  // subclass variables.
 4
 5  public class PolymorphismTest { 
 6     public static void main(String[] args) { 
 7        // assign superclass reference to superclass variable
 8        CommissionEmployee commissionEmployee = new CommissionEmployee(
 9            "Sue", "Jones", "222-22-2222", 10000, .06);
10
11        // assign subclass reference to subclass variable
12        BasePlusCommissionEmployee basePlusCommissionEmployee = ...