12.8 Programming Project #7:
An Employee Class Hierarchy
Background
The code that you wrote for the second Employee project only works for hourly
employees. Now that we have studied polymorphism, we can begin to make our
payroll program more general. The most important thing we will do is enable
polymorphism in our Employee class hierarchy, so that employee objects of different
types automatically behave correctly.
Objectives
• Continue gaining experience with object-oriented design
• Learn to create a class hierarchy that is enabled for polymorphism
• Learn to use polymorphism in a program.
The Program
We will rename Employee to HourlyEmployee, and then create two new classes,
Employee and SalariedEmployee, as depicted in the class diagram below.
(Items preceded by dashes are private, those preceded by a # are protected, and
public members start with a +. Static members appear underlined.)
Employee is an abstract class, meaning that it exists to hold what is common to all its
derived classes, and is not to be instantiated directly by users. For this reason, it has
no public constructors.
In addition to defining all things common to the derived employee classes, Employee
defines a virtual destructor and declares four pure virtual functions, which are
overridden in the derived classes (see the italicized functions in Employee above). All
of these functions have bodies in Employee except calcPay, and are called explicitly
from their derived counterparts. Note that readData functions as well as default
constructors have protected access. This is because we don’t want users to create
instances of the concrete, derived employee objects directly without complete
information.
Also, remember that base classes must always have a virtual destructor, even if the
body of that destructor is empty (which is what = default accomplishes here).
Finally, the parameterized constructors for the derived classes take all pertinent
parameters for objects of their type (which includes data common to all employees).
The key functions work as follows:
read
This static member function creates an empty, derived employee object and then calls
readData to initialize it. It returns a pointer to a new object, if data was read correctly,
or nullptr if there was an input error. For example, HourlyEmployee::read creates a
new, empty HourlyEmployee object on the heap, emp, say. and then calls emp-
>readData. HourlyEmployee::readData calls Employee::readData to read in the
common employee fields from a file, and then reads in the hourly wage and hours
worked. The pointer to the initialized object (or nullptr) is then returned.
readData
As explained above, this function first calls the base class implementation
of readData, and then reads data from the file for its type of object (HourlyEmployee
or SalariedEmployee).
write
This function works similarly to readData: it first calls Employee::write to write out
the common data to the file, then writes out the specific derived class data.
printCheck
This function first calls Employee::printCheck to print the common check header, then
prints the rest of the check according to the type of the object. See the sample output
below to see how SalariedEmployee checks should look.
calcPay
Hourly Employees: An hourly employee’s gross pay is calculated by multiplying the
hours worked by their hourly wage. Be sure to give time-and-a-half for overtime
(anything over 40 hours). To compute the net pay, deduct 20% of the gross for Federal
income tax, and 7.5% of the gross for state income tax.
Salaried Employees: A salaried employee’s gross pay is just their weekly salary value.
To compute the net pay for a salaried employee, deduct 20% of the gross for Federal
income tax, 7.5% of the gross for state income tax, and 5.24% for benefits.
The main() Function
Your driver will provide the same set of options as in the previous project. However,
your driver code should be somewhat simpler because you will now create a vector of
Employee pointers, and store the pointers to your objects in this vector. Add heap
pointers to the following employees to your vector:
HourlyEmployee(1, “H. Potter”, “Privet Drive”, “201-9090”, 40,
12.00);
SalariedEmployee(2, “A. Dumbledore”, “Hogwarts”, “803-1230”,
1200);
HourlyEmployee(3, “R. Weasley”, “The Burrow”, “892-2000”, 40,
10.00);
SalariedEmployee(4, “R. Hagrid”, “Hogwarts”, “910-8765”, 1000);
You can then use a simple for-loop to save each object’s data to the file.
Here is a sample execution of Option 1:
This program has two options:
1 – Create a data file, or
2 – Read data from a file and print paychecks.
Please enter (1) to create a file or (2) to print checks:1
Please enter a file name: employee.txt
Data file created … you can now run option 2.
The contents of the file employee.txt should be:
1
H. Potter
Privet Drive
201-9090
40
12
2
A. Dumbledore
Hogwarts
803-1230
1200
3
R. Weasley
The Burrow
892-2000
40
10
4
R. Hagrid
Hogwarts
910-8765
1000
When you run option 2, your program should create a new vector of Employee
pointers. Make four calls to
either HourlyEmployee::read or SalariedEmployee::read, according to the
same order that you wrote the objects in part 1. Add the pointers returned by read to
your vector. Then loop through the vector printing out the checks. Here is an execution
of Option 2:
This program has two options:
1 – Create a data file, or
2 – Read data from a file and print paychecks.
Please enter (1) to create a file or (2) to print checks:2
Please enter a file name: employee.dat
………………..UVU Computer Science
Dept……………………………
Pay to the order of H.
Potter………………………………$348.00
United Community Credit Union
……………………………………………………….
…………..
Hours worked: 40.00
HourlyWage: 12.00
………………..UVU Computer Science
Dept……………………………
Pay to the order of A.
Dumbledore………………………………$807.12
United Community Credit Union
……………………………………………………….
…………..
Salary: 1200.00
………………..UVU Computer Science
Dept……………………………
Pay to the order of R.
Weasley………………………………$290.00
United Community Credit Union
……………………………………………………….
…………..
Hours worked: 40.00
HourlyWage: 10.00
………………..UVU Computer Science
Dept……………………………
Pay to the order of R.
Hagrid………………………………$672.60
United Community Credit Union
……………………………………………………….
…………..
Salary: 1000.00
From the end user’s point of view, your program will work just as it did before.
