COMP90041 Project A Tic Tac Toe solution




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1 Background
This project is the first in a series of three, with the ultimate objective of designing and implementing (in
Java) the game of Tic Tac Toe. It is a two player game, and the rules are as follows:
1. The game begins with an empty, 3 × 3 grid.
2. The two players then take turns placing a mark in an empty grid cell. Player O will use the ‘O’
(letter ‘O’, not zero) mark and Player X will use the ‘X’ mark.
3. The game is over in either case: (i) one player has 3 marks in a sequence (vertically, horizontally,
diagonally, or anti-diagonally), or (ii) there are no empty cells left.
Below we show a run of the game, where Player O moved first and won the game by placing 3 ‘O’s in the
second row of the game grid.
| | | | | | | |O | |O | |O
—– —– —– —– —– —–
| | |O| |O| |O| |O| |O|
—– —– —– —– —– —–
| | | | | |X | |X |X|X O|X|X
(1) (2) (3) (4) (5) (6)
2 Your Task
For this first project, your task is to write a class named TicTacToe that will enable two players to play
a single game of Tic Tac Toe. To achieve this goal you will practise the use of instance variables and
methods through the following stages.
2.1 Initialise the Game (2 Marks)
Your TicTacToe class should have a main method. This method will create an object of the TicTacToe
class named game and call a method run to run a game:
TicTacToe game = new TicTacToe();;
Here the main method will only serve as a “testing method” for the TicTacToe class. Rather than creating
it in a separate “TicTacToeTest” class, we put it in the TicTacToe class to simplify the project.
The game running process will be handled in the run method, which you need to implement. Note that
you should make run an instance method of the TicTacToe class, not a static method. The same
applies for the methods described in the following sections.
The run method will start with printing out a welcome message and prompting for the two players’ names:
Welcome to Tic Tac Toe!
Enter Player O’s name:
Enter Player X’s name:
Note here Rose and Jack are user input, not part of the program output. You should add proper instance
(non-static) variables to TicTacToe to store the two players’ names, as well as accessors and mutators for
them. You may assume that there is no space character (‘ ’) in the player names.
2.2 Print the Game Grid and Make a Move (4 Marks)
Next, the game starts. The program will print out the game grid:
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You need to add a printGrid method to the TicTacToe class for printing out the game grid. You should
also add proper instance variables to keep track of what mark has been placed at each grid cell. For the
9 grid cells, you will need 9 instance variables (you can use an array to simplify this if you know how to
use it properly, but you are not required to do so in this project). At start the grid is empty. You should
initialise the instance variables properly to reflect this. Your printGrid method will access these instance
variables to determine what to print at each grid cell.
The run method will then prompt for player’s move. We assume that Player O always moves first.
Rose’s move:
1 1
Here a player’s move is represented by two integers in the range of {0, 1, 2} × {0, 1, 2}, where “0 0”
represents the top-left cell and “2 2” represents the bottom-right cell. You need to add a proper method
to update the instance variables that store the grid cell status after a user has make a move.
2.3 Loop through the Game (4 Marks)
Now add a loop to repeatedly prompt for the players to take turns and make moves. The game grid
should be printed out after each move. Here is an example execution after adding the loop:
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Rose’s move:
1 1
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Jack’s move:
2 2
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| |X
Rose’s move:
1 2
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| |X
Jack’s move:
2 1
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Rose’s move:
1 0
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Add an instance method named getGameState to the TicTackToe class that returns the current state of
the game after a player’s move. There are four cases: (i) Player O has won; (ii) Player X has won; (iii)
the game is a draw; (iv) the game can still continue. You should define proper constants to represent
these different states. Note: we define “draw” to be a state when the game grid is full and neither player
has won. You do not need to write a method that determines whether there is a draw before the game
grid is full.
When the game is finished, print out a message showing the game winner’s name (in the run method).
For example, in the game playing process above, the player Rose has three ‘O’s in the second row and
hence won the game:
Game over. Rose won!
If the game grid is full and no player has won, then print out that there is a draw:
Game over. It was a draw!
Please note that:
• You may assume that all user input is valid, that is, you do not need to consider user input errors.
• There is no blank line before the first line, i.e., no println before the welcome message is called.
• The last line should be a full line, i.e., “Game over. Rose won!” is printed out using println.
• You will be given a sample test input file test0.txt and the corresponding sample output file
test0-output.txt. When you run your program by the following command in a terminal (or
Windows command line):
java TicTacToe < test0.txt > my-output.txt
your program should produce a file name my-output.txt which should be exactly the same as
test0-output.txt. In this command, “< test0.txt” and “> my-output.txt” are called “input
redirection” and “output redirection.” They use the content in test0.txt as the command line
input, and print the program output into my-output.txt.
• Tests will be conducted on your program by automatically compiling, running, and comparing your
outputs for several test cases with generated expected outputs. These test cases used will be
different from the sample test file given. The automatic test will deem your output wrong
if your output does not match the expected output, even if the difference is just having an extra
space. Therefore, it is crucial that you generate your own test files and test your program
• The syntax import is available for you to use standard Java packages. However, please DO NOT
use the package syntax to customize your source files. The automatic test system cannot deal with
customized packages. If you are using Netbeans as the IDE, please be aware that the project name
may automatically be used as the package name. Please remove any lines of the form
package ProjA;
at the beginning of the source files before you submit them to the system.
• Please use ONLY ONE Scanner object throughout your program. Otherwise the automatic test
will cause your program to generate exceptions and terminate. The reason is that in the automatic
test, multiple lines of test inputs are sent all together to the program. As the program receives
the inputs, it will pass them all to the currently active Scanner object, leaving any remaining
Scanner objects with nothing to read, causing a run-time exception. Therefore it is crucial that
your program has only one Scanner object. Arguments such as “It runs correctly when I do
manual test, but fails under automatic test” will not be accepted.
3 Assessment
This project is worth 10% of the total marks for the subject.
Your Java program will be assessed based on correctness of the output as well as quality of code implementation. See LMS for a detailed marking scheme.
4 Submission
Your submission should have one Java source code file. You must name it, and upload it
to the Engineering School student server. Then, you can submit your work using the following command:
submit 90041 A *.java
You should then verify your submission using the following command:
verify 90041 A > feedback.txt
This will store the verification information in the file feedback.txt, which you can then view using the
following command:
more feedback.txt
You should issue the above commands from within the same directory as where the file is stored (to get
there you may need to use the cd “Change Directory” command). Note that you can submit as many
times as you like before the deadline.
How you edit, compile and run your Java program is up to you. You are free to use any editor or development environment. However, you need to ensure that your program compiles and runs correctly
on the Engineering School student server, using build 1.8.0 of Oracle’s (as Sun Microsystems has
been acquired by Oracle in 2010) Java Compiler and Runtime Environment, i.e., javac and java programs. Submit your program to the server a couple of days before the deadline to ensure that they work
(you can still improve your program). “I can’t get my code to work on the student server but it
worked on my Windows machine” is not an acceptable excuse for late submissions.
The deadline for the project is 4pm Monday 11th April 2016. The allowed time is more than enough
for completing the project. Penalties will apply on late submissions at 2 marks per day. Late submissions
after 4pm Thursday 14th April 2016 will NOT be accepted.
5 Individual Work
Note well that this project is part of your final assessment, so cheating is not acceptable. Any form of
material exchange, whether written, electronic or any other medium is considered cheating, and so is
the soliciting of help from electronic newsgroups. Providing undue assistance is considered as serious
as receiving it, and in the case of similarities that indicate exchange of more than basic ideas, formal
disciplinary action will be taken for all involved parties.