Android™ How to Program, Second Edition

G.10.1. Abstract Superclass Employee

Class Employee (Fig. G.16) provides methods earnings and toString, in addition to the get and set methods that manipulate Employee’s instance variables. An earnings method certainly applies generically to all employees. But each earnings calculation depends on the employee’s class. So we declare earnings as abstract in superclass Employee because a default implementation does not make sense for that method—there isn’t enough information to determine what amount earnings should return. Each subclass overrides earnings with an appropriate implementation. To calculate an employee’s earnings, the program assigns to a superclass Employee variable a reference to the employee’s object, then invokes the earnings