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Over the semester we are going to make a Tic-Tac-Toe (TTT) game. If we have time, we will ultimately make it graphical, but before we do that we will make a version that uses the console for input and output.

As a first step we'll make a class that models a TTT board. And, because I'm going to test your TTT board class by writing my own program that uses your class, I'm going to specify the public methods that you must write and how they should behave.

Specification

Write a class named TTTBoard. Its purpose is to model a Tic-Tac-Toe game board.

We will refer to each position of the TTT board as an ordered pair (r,c) where the upper-left position of the board is at (0,0) and r increases downward and c increases to the right. So, the following board has an X at position (2,1) and an O at position (1,0).

 | | -+-+- O| | -+-+- |X| 

The following public methods should be supported in TTTBoard:

 public TTTBoard(int size) public TTTBoard() public char get(int r, int c) public void set(int r, int c, char ch) public int size() public char winner() public String toString() 

One constructor should take an int parameter indicating the size of the TTT board to be used (in case someone wanted to play a variation of TTT where a player needed, say, four-in-a-row to win). The other constructor should take no arguments, indicating that a standard size 3 board should be used. If size is less than 1, your constructor should throw an IllegalArgumentException.

The method get should return the character that is at position (r,c) or a space character ' 'if no character is at that position. The method set should set position (r,c) to be character ch. It should not be considered an error to use set to change an already set character to another one, including back to a space. If (r,c) is out-of-bounds, throw an IndexOutOfBoundsException.

The method size should return the dimension of the TTT board. It will be whatever size was passed to the constructor, or 3 if no value was passed to the constructor. All values for r and c in the range 0..size()-1 should be legal for set and get.

The method winner should determine whether there are size() of the same character in a row, either horizontally, vertically, or diagonally. If there is, the found character should be returned, otherwise a space character ' ' should be returned. If more than one winning sequence is found, you may return any of them.

The method toString should return a string representation of the board. For example, the board shown above as a single string is " | | -+-+- O| | -+-+- |X| ". Notice that is used to advance the output to the next line, so even though this is a single string, when it is printed it will appear as five lines on the screen. For testing purposes it is essential that each row of output is exactly 2 * size() - 1 characters (not counting the ), that the returned string does not end in , and that it uses the same pattern of characters as the example board above.

Your class should have a public class constant DEFAULT_SIZE set to 3 so that code can easily know what the default size of boards are. (Look up "classes, constants" in your textbook index if you don't recall how and where to define them.)