CS 209 Sec. 52 Spring, 2006 Lab 6 - B: Inheritance Instructor: J.G. Neal

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1 CS 209 Sec. 52 Spring, 2006 Lab 6 - B: Inheritance Instructor: J.G. Neal Objectives. To gain experience with: 1. The creation of a simple hierarchy of classes. 2. The implementation and use of inheritance. 3. The implementation and use of an array of objects. 4. The use of the Java API Documentation. Notes: 1. This exercise correlates with Chapter 8 of the textbook. 2. The class hierarchy of this lab exercise program looks like the following: Level 1: Employee Level 2: HourlyEmployee SalariedEmployee UnionEmployee 3. You should be able to explain where inheritance is used in this Java program. 4. You should be able to explain where method overriding takes place in this program. 5. You should be able to explain the difference between the visibility modifiers. Lab Instructions: 1. This exercise is a continuation of Lab Exercise 6-A. 2. Extend your Lab 6-A program. You will modify and extend your Lab 6-A program as described in the following steps. 3. Modify the Main driver class as described below. Within the main method, declare and create an array of the Employee data type. This array will be able to hold instances of the Employee class and any of its subclasses. This is true because, in general, every instance of a subclass is also an instance of (of the type of) its parent class. Declare the array so that it consists of 50 cells, so that it can hold up to 50 Employee instances. Eliminate the variables named p1, p2, p3, p4, p5, p6. Totally eliminate the use of any of these variables from the program. You will need to keep and continue to use the single Employee variable p. Eliminate the two switch statements that deal with selecting among the variables p1, p2, p3, p4, p5, p6. Replace each of the switch statements with a one-line statement that uses the appropriate element of the array. This Lab Exercise Part B assumes that, as part of Lab 6-A, you already added code within Page 1 of 7

2 the while loop to prompt the user for the type of employee and input the type from the user. Be sure to present the list of available types to the user, namely (1) Hourly Employee, (2) Salaried Employee, and (3) Union Employee. Tell the user what to enter to specify the employee type. For example, you could show the numbers for the list items, and tell the user to enter the number of their choice. An alternative would be to have the user enter the first letter of the type name. This Lab Exercise assumes that you eliminated the following statement that was in the previously existing driver program from Lab 05 to create the employee object (instance). p = new Employee(nameStr, idnum, prate, hrs); You should have replaced the statement with code that creates the correct type of employee object (instance) based on the employee type that the user specified via their data entry (mentioned in the above bulleted item. The program should create an instance of the HourlyEmployee, SalariedEmployee, or UnionEmployee class, depending on which of these three types the user specified. The program should not create instances of the Employee class. If the user enters an illegal choice, then your program should create an HourlyEmployee as a default. As part of Lab Part A, you should have modified the for-loop that creates the final display list of all the employees of all types. This for-loop is after the while(true) loop and it iterates though only the actual (non-null) elements of the array. You should have modified the for-loop as follows: a. Replace the switch statement with a one-line statement that selects the correct element of the array. b. In the body of the for-loop, in the statement that concatenates to the variable outputstr2, you should have added code to also display the employee type on a separate line. The additional code must invoke the getemployeetype method for the object. c. Be sure that your display includes all the data on each employee. d. Keep the statement that appears after the for-loop and which uses a JOptionPane dialog to display the contents of outputstr2. 4. Create a new public class, called SalariedEmployee, that is a subclass of Employee. This new class must be in its own separate file. Create the new SalariedEmployee class in the same package (folder) that contains the Main class (file) and the Employee class. The SalariedEmployee class must inherit all the member variables of the Employee class. Do not declare any member variables in the SalariedEmployee class. The SalariedEmployee class must have a default public constructor that takes no parameters. This constructor must initialize the employeetype member variable; this constructor must assign a value of Salaried to the employeetype variable. The SalariedEmployee class must also have a public constructor that takes a value for each of the inherited member variables as parameter, except for employeetype. This constructor must have parameters corresponding to the member variables for: name, ID number, pay rate, and hours worked. This constructor must invoke the constructor of Page 2 of 7

3 the parent class to initialize the member variables. In this second SalariedEmployee constructor, minimize the number of member variables that are initialized within its own body..the SalariedEmployee class must have a public computepay method that calculates pay by multiplying the number of hours worked times the hourly pay rate, up to a limit of 40 hours. That is, SalariedEmployees do not get paid for overtime hours worked. They only get paid for the hours worked, up to a limit of 40 hrs per week. a. This class must have a public tostring method as in the HourlyEmployee class. 5. Create a new public class, called UnionEmployee, that is a subclass of Employee. This new class must be in its own separate file. Create the new UnionEmployee class in the same package (folder) that contains the Main class (file) and the Employee class. The UnionEmployee class must inherit all the member variables of the Employee class. Do not declare any member variables in the UnionEmployee class. The UnionEmployee class must have a default public constructor that takes no parameters. This constructor must initialize the employeetype member variable; this constructor must assign a value of Union to the employeetype variable. The UnionEmployee class must also have a public constructor that takes a value for each of the inherited member variables as parameter, except for employeetype. This constructor must have parameters corresponding to the member variables for: name, ID number, pay rate, and hours worked. This constructor must invoke the constructor of the parent class to initialize the member variables. In this second UnionEmployee constructor, minimize the number of member variables that are initialized within its own body. The UnionEmployee class must have a public computepay method that calculates the employee s pay using the following rules: a. A UnionEmployee's pay consists of: NormalTimePay + TimeAndHalfPay b. "Normal time pay" is computed at the employee s normal pay rate. This applies to the hours worked up to and including 40 hours. c. "Time and a half pay" is computed at 1.5 times the employee s normal pay rate. This applies to the additional hours worked that are in addition to the normal 40 hours. d. Example: If an employee s pay rate is $10.00 per hour and worked 60 hours in a week, the pay calculation for the employee is as follows: Amount at "normal time pay" rate: 1.0 * $10.00 * 40 hrs = $ Amount at "time and a half pay" rate: 1.5 * $10.00 * 20 hrs = $ Total pay (adding the two pay amounts): $ This class must have a public tostring method as in the HourlyEmployee class. 6. Compile, execute, and debug the program. Test and debug your program using a variety of input data that includes the use of all three subclasses. 7. Run the program and make window captures of the dialogs displaying all the different inputs and outputs. Page 3 of 7

4 8. Answer questions using the Java SDK Documentation, which you downloaded and installed on your computer as per the instructions in the course syllabus. First, bring up the index.html page in your web browser and scroll down a bit until you see the larger bold line API & Language Documentation. Click on the next hyperlinked text line, consisting of Java 2 Platform API Specification. Determine the answers to the questions listed below and report your answers in your ReadMe doc for this project. Using the Java 2 Platform API Specification, determine the answers to the following questions. When you report your answers in your ReadMe doc file, label your answers with the letters used below (a, b, c, etc.). i. Examine the documentation on the JOptionPane class. The JOptionPane class is an immediate subclass of what class? ii. Copy and paste the second paragraph of the JOptionPane documentation into your ReadMe file. iii. List the names of the four methods that are listed in the table right below the second paragraph. iv. How many different constructors (with different signatures) does the JOptionPane class have? v. How many different methods named showinputdialog (with different signatures) does the class have? vi. A JOptionPane object inherits methods from what four classes? List the names of the four classes. 9. Create batch file. Create a batch file as you did for the previous assignments so that your program can be executed without the use of NetBeans. Be sure that the batch file is within your top level NetBeans project folder. 10. Create ReadMe file. Using Microsoft Word, create a file named ReadMe. In this document, insert your name at the top, and on the next line insert the assignment number. Then enter any comments regarding the assignment and your program. Indicate whether you did the extra credit part of the assignment. Then insert several window captures of windows showing the inputs and outputs from the execution of the program. If you did the extra credit part of the assignment, be sure to state this in your ReadMe file. Also, include window captures that demonstrate the extra credit capabilities. Be sure the ReadMe document (file) is within your top level NetBeans project folder. Your ReadMe file must include your answers to the questions listed in Step 8 above. 11. Zip the project folder and all its contents. Create a zip file that contains the entire contents of your NetBeans project folder, including all sub-folders and files. Your project folder should contain your ReadMe file and batch file, as for previous project assignments. Change the name the zip file so that its name consists of your name along with the Page 4 of 7

5 assignment number, as follows: JohnJones-06.zip. Do not use spaces in the name of the file, use hyphens instead. 12. Extra Credit: In the main class for your project, write a new method named arraytostring that meets the following specifications: a. The method takes two parameters: (1) an array of type Employee and (2) the number of actual objects in the array (not the maximum number of elements). b. The method must iterate though the array of Employees and build up a string comprised of all the data on all the employees, each employee s data on a separate line. The string is built up using string concatenation. The employees must be numbered, starting with 1, since the string is intended for display purposes. c. The method must invoke the tostring method for each object to obtain the one-line version of all the data on each employee. d. The method must return the string that was built up by the method code, as described in the above paragraphs. In the main method of the main class, eliminate the statement (or any modified version of this statement): outputstr += count + ". " + p.tostring() + "\n"; Instead of the use of the above statement, to generate a text string comprised of the data on all the employee instances, use a call to the arraytostring method with correct actual parameters. Insert this method call in the correct manner and place in the program code. TO RECEIVE CREDIT FOR YOUR ASSIGNMENT: Submit the following for credit to Angel Drop Box for Exercise 6-B: a. The zip file containing your entire NetBeans project folder with all its subfolders and files. b. You must have a batch file to run your program without using NetBeans, and the batch file must be in your top level project folder. c. You must have a ReadMe file that contains your name at the top, the lab number, any comments regarding the assignment, and window captures to show the program execution. The ReadMe file must include your answers to the questions in Step 8 above. The ReadMe file must be in the top level project folder. d. You must submit your zip file to the Lab06-B Drop Box for this CS 209 course in Angel ( DUE DATE: Tuesday, March 14. EXAMPLE WINDOW CAPTURES FOR THE COMPLETED PROGRAM: Page 5 of 7

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