G.4. Relationship between Superclasses and Subclasses

We now use an inheritance hierarchy containing types of employees in a company’s payroll application to discuss the relationship between a superclass and its subclass. In this company, commission employees (who will be represented as objects of a superclass) are paid a percentage of their sales, while base-salaried commission employees (who will be represented as objects of a subclass) receive a base salary plus a percentage of their sales.

We create an example that sets the CommissionEmployee instance variables to private to enforce good software engineering. Then we show how the BasePlusCommissionEmployee subclass can use CommissionEmployee’s public methods to manipulate (in a controlled manner) the private instance variables inherited from CommissionEmployee.