Week 6: Interfaces and Abstract Classes – iLab
iLab 6 of 7: Abstract Class and Polymorphism
i L A B O V E R V I E W
Scenario and Summary
We have two separate goals this week:
We are going to create an abstract Employee class and an abstract calculatePay method. The abstract Employee class will prevent a programmer from creating an object based on Employee. Only objects based on Salaried and Hourly will be allowed. The abstract calculatePay method in Employee will force the child classes to implement calculatePay.
We are going to implement Polymorphism and dynamic binding by creating generalized methods that accept generalized Employee objects to collect input and display information. However, in the main method we will pass derived objects of the Employee class into the methods.
Deliverables
Due this week:
Capture the console output window and paste it into a Word document.
Zip the project files.
Put the zip file and screenshots (Word document) in the Dropbox.
i L A B S T E P S
STEP 1: Understand the UML Diagram
Notice in the updated UML diagram that the Employee class is designated as abstract by having the class name Employee italicized. Also, the calculatePay method is italicized, which means that it is an abstract method and needs to be implemented in the derived classes.
Employee #firstName : string #lastName : string #gender : char #dependents : int #annualSalary : double #benefit : Benefit -static numEmployees : int = 0 +Employee() +Employee(in fname : string, in lname : string, in gen : char, in dep : int, in benefits : Benefit) +static getNumEmployees() : int +CalculatePay() : double +displayEmployee() : void Benefit -healthinsurance : string -lifeinsurance : double -vacation : int +Benefit() +Benefit(in hins : string, in lins : double, in vac : int) +displayBenefits() : void Salaried -MIN_MANAGEMENT_LEVEL : int = 0 -MAX_MANAGEMENT_LEVEL : int = 3 -BONUS_PERCENT : double = 10 -managementLevel : int +Salaried() +Salaried(in fname : string, in lname : string, in gen : char, in dep : int, in sal : double, in ben : Benefit, in manLevel : int) +Salaried(in sal : double, in manLevel : int) +CalculatePay() : double +displayEmployee() : void Hourly -MIN_WAGE : double = 10 -MAX_WAGE : double = 75 -MIN_HOURS : double = 0 -MAX_HOURS: double = 50 -wage : double -hours : double -category : string +Hourly() +Hourly(in wage : double, in hours : double, in category : string) +Hourly(in fname : string, in lname : string, in gen : char, in dep : int, in wage : double, in hours : double, in ben : Benefit, in category : string) +CalculatePay() : double +displayEmployee() : void
STEP 2: Create the Project
Create a new project and name it CIS247B_WK6_Lab_LASTNAME. Copy all the source files from the Week 5 project into the Week 6 project.
Before you move on to the next step, build and execute the Week 6 project.
STEP 3: Modify the Employee Class
Make the Employee class abstract.
Define calculatePay as an abstract method.
STEP 4: Modify the Hourly Class
Implement the calculatePay method. Since calculatePay is not declared as an abstract method in Employee, all subclasses of Employee must provide an implementation for calculatePay. Unlike the Salaried class, the Hourly class does not currently have an implementation for calculatePay and this will cause an error!
STEP 5: Modify the Main Class – Create Generalized Input Methods
In your Main class, create a method called collectEmployeeInformation that accepts as an argument an Employee object and prompts the user for all the employee attributes, retrieves the attributes, makes any necessary conversions, and then sets the attribute value in the object. Remember you may pass both Salaried and Hourly objects into this method. Therefore it will be necessary to determine which type of object you are deal with, at runtime, using the getClass method. The following is an example of how you might use the getClass method:
if (employee.getClass() == Salaried.class){ // Put code here that is specific to Salaried objects } else { // Put code here that is specific to Hourly objects }
Once you have determined the type of object you are dealing with, you will also need to cast that object to the correct type in order to access its class-specific methods. In order to cast a general Employee object to a Salaried object and access one of its class-specific methods, you would do the following:
((Salaried)employee).methodInSalariedClass;
We are also going to implement error handing this week using a try/catch block. Specifically, you should wrap the code used to acquire and set the life insurance amount and vacation days in try-catch blocks as shown below. The “try” portion of the code looks for an error. If an error occurs parsing the integer, it jumps down to the “catch” portion of the code and displays the error message. Because badInput is still true, it loops back to the “do” and starts over. Once the integer is parsed correctly, badInput is set to false so it exits the loop and correctly sets the value for vacation.
boolean badInput = true; String strVacation = “”; //Must be initialized vacation = 0; //Must be initialized do { try { strVacation = JOptionPane.showInputDialog(“Vacation: “); vacation = Integer.parseInt(strVacation);//Possible Error badInput = false; } catch (Exception ex) { JOptionPane.showMessageDialog(null,strVacation + ” is not an integer”,”Error”,JOptionPane.PLAIN_MESSAGE); } } while(badInput);
STEP 6: Modify the Main Class – Create a Generalized Output Method
Create a method called displayEmployeeInformation that accepts an Employee object, provides an output header string, and then displays Employee information.
STEP 7: Modify the Main Class – Create a Display Number Employee Method
Create a method called displayNumberOfEmployees to display the number of employee objects.
STEP 8: Modify the Main Method
Create an array of employee objects with: Employee employeeList[] = new Employee[2];
For the first employeeList index, create a Salaried employee.
Call the collectEmployeeInformation method, passing in the Salaried object.
Use the displayEmployeeInformation method to display the object’s state.
Use the displayNumberEmployees method to display the total number of Employees created. Remember, this includes both Salaried and Hourly employees.
For the second employeeList index, create an Hourly employee.
Repeat Steps 3-5 for the Hourly object.
As an educational exercise, you can try to create an Employee object to verify that an error will occur.
STEP 9: Compile and Test
When done, compile and execute your code, and debug any errors until your code is error-free.
Check your output to ensure that you have the desired output, modify your code as necessary, and rebuild.
All of the output values should match last week’s output.
CIS/247A CIS247A CIS-247A CIS247 A CIS 247 A
CIS/247B CIS247B CIS-247B CIS247 B CIS 247 B
CIS/247C CIS247C CIS-247C CIS247 C CIS 247 C
CIS/247D CIS247D CIS-247D CIS247 D CIS 247 D
Lab6 Lab 6 Week 6 Week6 Week6 Lab
–iqrajavaid
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