Chapter 3, Problem 4R

Modified Program:

//Define TicTacToe class

public class TicTacToe

{

  //Declare and initialize the required variables

public static final int X = 1, O = -1;

public static final int EMPTY = 0;

//Declare the two dimensional game board variable

private int board[][] = new int[3][3];

//Declare current player variable

private int player;

//Define default constructor

public TicTacToe( )

{

/*Call clearBorad() method to clear the game board. */

  clearBoard( );

}

  //Define clearBoard() method

public void clearBoard( )

{

  //Loop executes until 3 rows

  for (int i = 0; i < 3; i++)

  //Loop executes until 3 columns

  for (int j = 0; j < 3; j++)

  //Clear each and every cell

board[i][j] = EMPTY;

//Assign first player is "X"

player = X;

}

  //Modified method

  //Define modified putMark() method

public void putMark(int i, int j) throws IllegalStateException

  {

  //Check whether the rows and column missing

  if ((i < 0) || (i > 2) || (j < 0) || (j > 2))

  //Throw an IllegalStateException

throw new IllegalStateException("Invalid  board position");

  //Check whether the game board is not empty

  if (board[i][j] != EMPTY)

  //Throw an IllegalStateException

throw new IllegalStateException("Board position occupied");

  //Assign current player into board

board[i][j] = player;

  //Change the players

player = -player; // switch players (uses fact that O = - X)

  }

/*Define the isWin() method to checks whether the board configuration is a win for given player.*/

  public boolean isWin(int mark)

  {

/*Return the board configuration for rows and columns. */

return ((board[0][0] + board[0][1] + board[0][2] == mark*3) || (board[1][0] + board[1][1] + board[1][2] == mark*3) || (board[2][0] + board[2][1] + board[2][2] == mark*3) || (board[0][0] + board[1][0] + board[2][0] == mark*3) || (board[0][1] + board[1][1] + board[2][1] == mark*3) || (board[0][2] + board[1][2] + board[2][2] == mark*3) || (board[0][0] + board[1][1] + board[2][2] == mark*3) || (board[2][0] + board[1][1] + board[0][2] == mark*3));

  }

/* Define winner() method to returns the code for winning players or indicates "0" for tie the game or unfinished game.*/

public int winner( )

{

//Call the isWin() method to check the winning player is "X". */

if (isWin(X))

  //Returns the code "X" for winning players

  return(X);

//Otherwise, call the isWin() method to check the winning player is "O". */

else if (isWin(O))

  //Returns the code "O" for winning players

  return(O);

//Otherwise, exit the game

else

  return(0);

}

/*Define toString() method to returns the current board for showing the simple character string. */

public String toString()

{

  //Create an object for StringBuilder

StringBuilder sb = new StringBuilder();

//Loop executes until 3 rows

for (int i=0; i<3; i++)

{

  //Loop executes until 3 columns

  for (int j=0; j<3; j++)

  {

  //Match the character in board

  switch (board[i][j])

  {

/*If the row and column contains "X"...