Java Polymorphic processing: Incorrect output?

Question

In the following class I am trying to print details of Employees in a payroll system. Note that Porter, Pharmacist and Surgeon all inherit from Employee.

However it is only repeatedly printing details of the first employee added to the array. I know the expected output but I am unable to reproduce it.

Class:

public class PayrollManager {

    public static final int HOURS_PER_WEEK = 35;

    public static Employee[] employees = new Employee[6];

    public static void main(String[] args) {

        // create all employees
        Employee generalEmployee = new Employee("Odd", "Jobbie", 10.50);
        Employee porter1 = new Porter("Ivana", "Patient", 10.50, "Royal");
        Employee porter2 = new Porter("Amanda", "Pushabed", 10.50, "BCH");
        Employee surgeon1 = new Surgeon("Jack", "Ripper", 55.25, "Renal",
                650.00);
        Employee surgeon2 = new Surgeon("Edward", "Lister", 55.25, "Vascular",
                800.00);
        Employee pharmacist = new Pharmacist("Poppy", "Pill", 30.50, 7, 750);

        // call method to handle adding the employees to the list
        addEmployeeToList(generalEmployee);
        addEmployeeToList(porter1);
        addEmployeeToList(porter2);
        addEmployeeToList(surgeon1);
        addEmployeeToList(surgeon2);
        addEmployeeToList(pharmacist);

        // show all employees
        displayAllEmployees();
        System.out.println();
        // run payroll
        processWeeklyPayroll();

    }// end of main

    /**
     * Method to add an Employee to an array
     * 
     * @param e
     */
    public static void addEmployeeToList(Employee e) {

        for (int loop = 0; loop < employees.length; loop++) {
            // check there is a space
            if (employees[loop] == null) {
                // add it to free space
                employees[loop] = e;

            }
        }

    }

    public static void displayAllEmployees() {

        for (Employee e : employees) {

            if (e != null) {

                e.displayAll();
                System.out.println();
            }
        }
    }

    public static void processWeeklyPayroll() {

        for (Employee e : employees) {

            if (e != null) {

                e.calculateWeeklySalary(HOURS_PER_WEEK);
                // line break
                System.out.println();
            }
        }

    }

}

Current Output:

[Employee] Odd Jobbie 10.500000
[Employee] Odd Jobbie 10.500000
[Employee] Odd Jobbie 10.500000
[Employee] Odd Jobbie 10.500000
[Employee] Odd Jobbie 10.500000
[Employee] Odd Jobbie 10.500000

Odd Jobbie [Base Rate Employee] : 35.000000hrs * £10.500000= £367.500000
Odd Jobbie [Base Rate Employee] : 35.000000hrs * £10.500000= £367.500000
Odd Jobbie [Base Rate Employee] : 35.000000hrs * £10.500000= £367.500000
Odd Jobbie [Base Rate Employee] : 35.000000hrs * £10.500000= £367.500000
Odd Jobbie [Base Rate Employee] : 35.000000hrs * £10.500000= £367.500000
Odd Jobbie [Base Rate Employee] : 35.000000hrs * £10.500000= £367.500000

Note that the expected output should be printing details of each member of test data, i.e. each pharmacist, surgeon etc...

My guess is that your variables are all static. Please show the relevant classes - ideally a short but complete program demonstrating the problem. (And ideally, stop using double for currency values...) — Jon Skeet
– Jon Skeet, Commented Jun 5, 2014 at 17:34

Valdrinium · Accepted Answer · 2014-06-05 17:38:33Z

1

This is the culprit:

public static void addEmployeeToList(Employee e) {

    for (int loop = 0; loop < employees.length; loop++) {
        // check there is a space
        if (employees[loop] == null) {
            // add it to free space
            employees[loop] = e;

        }
    }

}

It just sets all the employees in the list to the argument with which the function is first called; when you first call it, employees is full of null elements, so the condition is always true; but the second, third etc. time you call it, all the elements are set to the generalEmployee.

A quick fix would be:

public static void addEmployeeToList(Employee e) {

    for (int loop = 0; loop < employees.length; loop++) {
        // check there is a space
        if (employees[loop] == null) {
            // add it to free space
            employees[loop] = e;
            break;
        }
    }

}

But I strongly suggest using an ArrayList.

ArrayList<Employee> employees = new ArrayList<Employee>(); //here you declare a dinamically resizing list.
employees.add(e) //this is how you add a new Employee to the list.

answered Jun 5, 2014 at 17:38

Valdrinium

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1 Comment

user3287264 Over a year ago

Thank you, Yeah I would prefer to do an arrayList but the exercise specifically stated to use arrays!

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