Java™ How To Program (Early Objects), Tenth Edition

10.5.1 Abstract Superclass Employee

Class Employee (Fig. 10.4) provides methods earnings and toString, in addition to the get methods that return the values of Employee’s instance variables. An earnings method certainly applies generically to all employees. But each earnings calculation depends on the employee’s particular class. So we declare earnings as abstract in superclass Employee because a specific default implementation does not make sense for that method—there isn’t enough information to determine what amount earnings should return.

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 1   // Fig. 10.4: Employee.java 2   // Employee abstract superclass. 3  4   public abstract class Employee 5   { 6      private final String firstName; 7      private final ...