CS I Laboratory # 4
Let the Dice Roll!

Due: by Friday, March 14th
Objective: To gain experience implementing a class.

The Assignment Overview

For this lab, you are to implement a Die class. Your Die class will have methods for constructing, rolling, getting the current roll of the die, and some ObjectDraw-like methods such as move, getX, contains, etc. We will supply you with a simple Yahtzee game (file Yahtzee.java) that uses your Die class. When the Yahtzee program runs, it will look like the following figure.

Getting Started

1. First you need to locate a free computer in either Wright 112 or 339. Create a new folder "lab4" on the " Student Z: " drive in the folder "cs061" which you created in lab 1.

2. Start Internet Explorer by Start | Programs | Internet | Internet Explorer and go to http://www.cns.uni.edu/~jacobson/061/lab4.

3. Download each of the files "objectdraw.jar", "lab_4.gpj", "Die.java," and "Yahtzee.java" by right-clicking on the name of each file and selecting "Save Target As". Save these files to your newly created "Z:\cs061\lab4" folder. The Die.java file contains the template for a Die class.

4. Start jGrasp by double-clicking on the lab_4.gpj project file that you downloaded to your new lab4 folder. By using this project file you sets up the correct Compiler and run-time settings for the objectdraw package.

5. Click on the "Project" tab at the bottom of the upper-left-hand sub-window of jGrasp. Double click "Yahtzee.java" and "Die.java" file. Enlarge the "Die.java" window.

6. When compiling, compile from the "Yahtzee.java" window. It will compile both of the two different .java files: "Yahtzee.java" and "Die.java" files.

Part A

As with the last lab, we want you to practice incrementally developing the Die class. To encourage this approach, we have commented out several sections of the "Yahtzee.java" file. Initially, only the "begin" method is not commented out. Since "begin" only uses the Die constructor, you can develop, test, and debug only the constructor to start. Once the constructor is working, move on to part B of the assignment.

The constructor is called from within "Yahtzee.java" as:

die1 = new Die(DIE_LEFT, TOP_DIES_TOP, canvas);
where the first two parameter are the x and y locations (both of type double) of the die, and the third is a reference to the DrawingCanvas object, called "canvas," associated with the WindowController. To keep the Die class simple, assume that a die is always displayed as a 30 x 30 FramedRect, so we do not pass any "size" parameters.

A template for the Die constructor is already in the Die.java file. Your Die constructor should do the following things:

• randomly decide the face value of the die (an integer between 1 and 6) and assign it to an instance variable
• construct appropriate ObjectDraw objects (and assign them to instance variables) that display the die

Part B

Once you get part A working, uncomment the Yahtzee.java code associated with part B. This code requires you to implement the following Die methods in the Die.java file.

Method Name	Type of value returned	Parameters and (types)	Description
getX	double	none	Returns the x coordinate of the die's left edge
roll	none	none	Randomly changes the die value to a new value between 1 and 6
getRoll	int	none	Returns the current die value

After implementing all of the above Die methods, recompile the Yahtzee.java code. Now, run the Yahtzee program. The "Reroll" button should work, and you should observe the dice values changing, but you will not be able to drag the dice. Debug the methods associated with part B before working on part C.

Part C

Once you get part B working, uncomment the Yahtzee.java code associated with part C. This code requires you to implement the following Die methods in the Die.java file.

Method Name	Type of value returned	Parameters (and their types)	Description
contains	boolean	Location	Returns true if the Location parameter is within the Die object on the screen; otherwise return false.
move	none	xOffset (double) yOffset (double)	Repositions the Die object on the screen by the specified xOffset and yOffset

After implementing all of the above Die methods, recompile the Yahtzee.java code. When you run the Yahtzee program, it should be fully functional, i.e., the dice should be dragable, etc.

Turning in your program

The submission procedure is basically the same as last week.

• Turn in hard-copy printouts of the Yahtzee.java and Die.java files. Make sure you included your name, section, and current date in a comment at the start of the programs.
• Turn in a 3.5" floppy disk containing the files: Yahtzee.java, Die.java, objectdraw.jar, lab_4.gpj.
• Turn in printouts of the running program that demonstrate that it works.

Hard-copies, output, and the floppy disk should be turned into the instructor inside the large vanilla envelope. Labs are due before you leave for spring break.

Good luck and have fun!

Tips for success on Lab 4

• Start the lab early so you have lots of opportunity to ask questions of your instructor or the TAs. However, you should have at least struggled with understanding the lab before seeking help!!!
• Look at relevant code examples discussed in class and in the Williams College Manuscript. For this lab, the Tshirt class discussed and linked to from the http://www.cns.uni.edu/~jacobson/061 web site would be especially useful to study carefully.
• Read the lab and try to write the methods for each part on PAPER BEFORE sitting down at the computer! You'll make fewer mistakes, so the lab will actually require you less time to complete.