CSE115 Fall 2007

CSE115 Fall 2007 - Lab #4

Working from home

If you are working from home you must download a current copy of the Classlibs.jar file
WINDOWS: download and place in your C:\projects\CSE115\Classlibs\Fall2007 directory
OS X/Linux/Unix/etc: download and place in your /projects/CSE115/Classlibs/Fall2007 directory

Introduction

In this lab you will practice instantiating classes, calling methods, and using local variables to swap the properties of two objects.

Objectives

The high-level objectives of this lab are to have you,

edit some Java source code files using Eclipse, and
compile, debug and run a small Java program.

The following are the new concepts covered in this lab:

defining non-constructor methods
declaring local variables
assigning values to variables
calling a method (sending a message) with arguments
getting a value from a method call (receiving a value in reply to a message)
writing javadoc comments

Assignment Specifications

For this lab we have built a framework which creates a graphical user interface (GUI, pronounced "gooey") for which you are going to provide the functionality. The program will display two separate areas (called "drawing canvases"), each of which will contain an object of a certain color, represented on-screen using a particular graphic (either an ellipse or a rectangle), which behaves in a particular way.

The GUI has three buttons. Pressing the "swap colors" button will interchange (swap) the colors of the two objects. Pressing the "swap behaviors" button will interchange (swap) the behaviors of the two objects. Finally, "swap graphics" will interchange (swap) the graphic used to draw the two objects.

Each time you click on one of the three buttons, exactly one of the three properties (color, behavior, graphic) is exchanged between the two objects, and the other two stay the same.

Your task is just to complete the definitions of the three methods which are to carry out the swap of the property values.

In the code, the objects whose properties you must swap are instances of the class lab4lib.ChangeableShape.

Helpful Hints

Read through the entire lab before you start working, so that you know what to expect. Make sure you save your work often, and keep track of what you are expected to submit.

When you are confident about the design, start writing your program. Begin by just getting the GUI window to appear. Then add small parts to your program, making sure that they work as you expect them to. This idea of writing your program incrementally will be very important as your programs get larger and harder to debug, so getting into a good habit now will save you a great deal of time in the future.

Preparatory work

In order to be able to carry out the tasks required during your lab session, you must come prepared. Do the following before coming to your lab session:

Reading
Make sure you have read and understood chapters 1, 2 and 3 of the Alphonce-Decker notes. Also make sure you have reviewed your lecture notes.
Try the demo

Make sure you have tried the demo, so that you understand what the behavior of your program should be in the end. If the applet does not load then you need to install the Java plug-in for your browser.

Note: Not all department browsers have the plug-in installed.

Note: Decompiling the demo is a flagrant violation of the policy on academic integrity and will minimally result in immediate failure in the course.

Lab tasks

At your lab session your teaching assistant will briefly discuss how to carry out each of the tasks below. She or he will also be available to answer questions you might have. You must carry out each of the following tasks.

Log in

Start Eclipse

Get project skeleton
Retrieve the Lab4 project skeleton from the LabSkeletons respository.
Disconnect the project from the repository
Make sure you disconnect your local copy of the Lab 4 project skeleton from the repository.
Look at what you have...

In the Lab4 project you will see two packages: lab4 and lab4support. The only file you need to worry about is the PropertySwapper class defined in the lab4 package.

This class has three methods defined with empty bodies. Your job is to complete their definitions so that they swap the relevant property of the two lab4lib.ChangeableShape objects (or shapes, for short) in the left and right drawing canvases. These methods are called when the corresponding button is clicked in GUI.

Next, see what's already available to you: run the program by creating an instance of lab4.Driver in DrJava's interactions pane. When the GUI comes up, notice that clicking the buttons has no effect.

...think ahead...

You need to write code for each of the following methods:
public void swapBehaviors() {
	//TODO Complete the body of this method to swap behaviors of the shapes.
}

public void swapColors() {
	//TODO Complete the body of this method to swap colors of the shapes.
}

public void swapGraphics() {
	//TODO Complete the body of this method to swap graphics of the shapes.
}
If you reflect a bit on the problem, you should realize that although a different property value is being swapped between the two shapes in each method, the steps required to swap a property value should be essentially the same in each case.

...but start with just one method
Suppose you start with the swapColors method. This method is called automagically whenever the button labelled "swap colors" is pressed. Any code you put in the body of this method will be executed whenever the button is pressed.

Since you want to swap the colors of the two shapes when the "swap colors" button is pressed, you need to add to the body of this method the Java code which will do exactly that: swap the colors of the two shapes.

But how can we do this? First, we need to be able to communicate with the two shapes: we need to get references to them! To avoid using any Java languages features that you have not been exposed to yet, you will need to do a little bit of extra work here, but only using things you already know about.

Instances of the lab4lib.ShapeHolder class provide two methods you will need; their method headers are:
public lab4lib.ChangeableShape getLeftShape()

public lab4lib.ChangeableShape getRightShape()
They return references to the shapes in the left and right drawing canvases, respectively. The references are to objects of type lab4lib.ChangeableShape.

Each lab4lib.ChangeableShape provides methods which you can use to both get and set the values of its properties; the headers of these methods are:
	public void setColor(java.awt.Color color)

	public java.awt.Color getColor()

	public void setBehavior(Behavior behavior)

	public Behavior getBehavior()

	public void setGraphic(Graphic graphic)

	public Graphic getGraphic()
Once you have written some code to swap colors, test your solution by running the program and make sure that the color swaps when you exchange the shapes' colors.

If your method doesn't do what it should, go back and fix it. If you need help, talk to your TA.

Once you have your color-swapping method all finished, write some nice JavaDoc comment for the method explaining what the method does (not how). Your TAs will show you how to do this in more detail.

Move on

Now try one of the other methods, like the behavior-swapping method.

Once you have your behavior-swapping method all finished, write some nice JavaDoc comment for the method explaining what the method does (not how).

Move on to the last method. JavaDoc it appropriately.

Finally, add JavaDoc comments for the class itself.

Grading (rough, and subject to change)

As a rough guideline, you can expect 30 points to come from your JavaDocs, 60 points to come from coding of the three metohds, and 10 points to come from proper submission.

What you hand in

Once you are ready to submit, export your solution as a jar file. Name your jar file Lab4.jar

Use the electronic submission command that corresponds to your recitation. For instance students in section A1 will submit by typing,

submit_cse115a1 Lab4.jar

at the Linux prompt.

Due dates

You have one week from the meeting of your lab to submit your solution. For example, if your recitation meets on Wednesday, September 26^st then you must submit the lab by 11:59 PM on Tuesday, October 2^nd. The due dates are summarized in the table below. If you submit more than once, the later submission will simply overwrite the previous one.

Date of lab	Due date for electronic submission
Tuesday, September 25	Monday, October 1
Wednesday, September 26	Tuesday, October 2
Thursday, September 27	Wednesday, October 3
Friday, September 28	Thursday, October 4

Notice

This lab was designed and written by Carl Alphonce. It is inspired by a lab originally designed and written by Stephen Wong.