Polymorphism - Java Software Solutions: Foundations of Program Design - page 496

However, the descendants of StaffMember each provide their own specific definition
for pay . By defining pay abstractly in StaffMember , the payday method of Staff
can polymorphically pay each employee.
This is the essence of polymorphism. Each class knows best how it should
handle a specific behavior, in this case paying an employee. Yet in one sense it's
all the same behavior—the employee is getting paid. Polymorphism lets us treat
similar objects in consistent but unique ways.
The Volunteer class shown in Listing 10.4 represents a person that is not
compensated monetarily for his or her work. We keep track only of a volunteer's
basic information, which is passed into the constructor of Volunteer , which in
turn passes it to the StaffMember constructor using the super reference. The
pay method of Volunteer simply returns a zero pay value. If pay had not been
LISTING 10.4
//********************************************************************
// Volunteer.java Author: Lewis/Loftus
//
// Represents a staff member that works as a volunteer.
//********************************************************************
public class Volunteer extends StaffMember
{
//-----------------------------------------------------------------
// Constructor: Sets up this volunteer using the specified
// information.
//-----------------------------------------------------------------
public Volunteer (String eName, String eAddress, String ePhone)
{
super (eName, eAddress, ePhone);
}
//-----------------------------------------------------------------
// Returns a zero pay value for this volunteer.
//-----------------------------------------------------------------
public double pay()
{
return 0.0;
}
}