CareerCup

Here is the fully working Java code for 1 player vs computer Tic Tac Toe game.
Compile it. Run it!

import java.util.Random;
import java.util.Scanner;
import java.io.*;
class Player
{
	private int score;
	private String name;
	Player()
	{
		name="Unknown";
		score=0;
	}
	Player(String name)
	{
		this.name=name;
		score=0;
	}
	public void addScore(int add)
	{
		score+=add;
	}
	public int getScore()
	{
		return score;
	}
	public String getName()
	{
		return name;
	}
}
class Board
{
	private final int size=3;
	private boolean gameOver;
	private boolean win;
	private int noOfMoves;
	private char[][] matrix=new char[size][size];
	Board()
	{
		int i,j;
		for(i=0;i<size;i++)
			for(j=0;j<size;j++)
				matrix[i][j]='.';
		gameOver=false;
		win=false;
		noOfMoves=0;
	}
	public void show()
	{
		int i,j;
		for(i=0;i<size;i++)
		{
			for(j=0;j<size;j++)
				System.out.print(" "+matrix[i][j]);			
			System.out.println();
		}
		System.out.println();
	}
	public boolean isGameOver()
	{
		return gameOver;
	}
	public boolean won()
	{
		return win;
	}
	public int playerMove(int x,int y)//1 player game against Computer
	{
		if(x<0 || y<0 ||x>=size || y>=size)
			return -1;//invalid move;
		if(matrix[x][y]=='O' || matrix[x][y]=='X')
			return -1;//invalid move
		matrix[x][y]='X';
		noOfMoves++;
		return 0;
	}
	public void computerMove()//1 player game against Computer
	{	//random move
		Random rand=new Random();
		int x,y;
		x=rand.nextInt(size);
		y=rand.nextInt(size);
		while(matrix[x][y]=='X' || matrix[x][y]=='O')
		{
			x=rand.nextInt(size);
			y=rand.nextInt(size);
		}
		matrix[x][y]='O';
		noOfMoves++;
	}
	public void setWon(char c)
	{
		if(c=='.')
			return;
		if(c=='X')
			win=true;
		else
			win=false;
		gameOver=true;
	}
	public void check()
	{
		int i,j;
		boolean f;
		for(i=0;i<size;i++)
		{
			j=1;
			if(matrix[i][0]!='.')
				for(;j<size;j++)//ith row check
					if(matrix[i][j]!=matrix[i][j-1])
						break;
			if(j==size)
			{
				System.out.println("row "+i+" crossed");
				setWon(matrix[i][0]);
				return;
			}
			j=1;
			if(matrix[0][i]!='.')
				for(;j<size;j++)//ith column check
					if(matrix[j][i]!=matrix[j-1][i])
						break;
			if(j==size)
			{
				System.out.println("col "+i+" crossed");
				setWon(matrix[0][i]);
				return;
			}
		}
		//diagonals
		i=1;
		if(matrix[0][0]!='.')
		for(;i<size;i++)
			if(matrix[i][i]!=matrix[i-1][i-1])
				break;
		if(i==size)
		{
			System.out.println("first diagonal "+i+" crossed");
			setWon(matrix[0][0]);
			return;
		}
		i=1;
		if(matrix[0][size-1]!='.')
		for(;i<size;i++)
			if(matrix[i][size-1-i]!=matrix[i-1][size-i])
				break;
		if(i==size)
		{
			System.out.println("second diagonal "+i+" crossed");
			setWon(matrix[0][size-1]);
			return;
		}
		if(noOfMoves>=size*size)
		{
			gameOver=true;
			win=false;
		}
		return;
	}
}
class TTT
{
	public static void main(String args[])
	{
		Scanner sc=new Scanner(System.in);
		Board board=new Board();
		Player player=new Player();
		int x,y;
		while(!board.isGameOver())
		{
			board.show();
			x=sc.nextInt();
			y=sc.nextInt();
			while(board.playerMove(x,y)==-1)
			{
				System.out.println("Invalid input. Enter again!");
				x=sc.nextInt();
				y=sc.nextInt();		
			}
			board.check();
			if(!board.isGameOver())
			{
				board.computerMove();
				board.check();
			}
		}
		board.show();
		if(board.won())
			System.out.println("Congrats! You won!!!!");
		else
			System.out.println("You lose! Go practice some more.");
	}
}

//Winner will be declared in constant time, no need to run loops to check winner on each move.

//This is main class to run a sample case
public class TicTacToeSample {
	public static void main(String[] args) {
		try {
			final Board board = new Board(3);
			Player X = new Player("X", board);
			Player Y = new Player("Y", board);
			
			X.takePosition(0, 0);
			Y.takePosition(1, 1);
			X.takePosition(2, 0);
			Y.takePosition(2, 0);
			Y.takePosition(1, 0);
			X.takePosition(2, 2);
			Y.takePosition(1, 2);
			X.takePosition(2, 1);
		} catch (WinnerException e) {
			System.out.println(e.getMessage());
		}
	}
}

class Board{

	private final Player[][] board;
	private final int size;
	public Board(int size){
		this.size = size;
		this.board = new Player[size][size];
	}	
	public int getRows() {
		return size;
	}
	public int getCols() {
		return size;
	}
	public int getDiagonals() {
		return 2;
	}
	public void setOnwer(Player player, int row, int col) throws IllegalStateException {
		if(board[row][col] == null){
			board[row][col] = player;
		}else{
			throw new IllegalStateException("Position already taken by player " + board[row][col]);
		}		
	}
	public Player getOnwer(int row, int col) {
		return board[row][col];
	}
	public int totalPositions() {
		return size;
	}
	
}

@SuppressWarnings("serial")
class WinnerException extends Exception{
	public WinnerException(String msg) {
		super(msg);
	}	
}

class Player{	
	private final String name;	
	private final Board board;	
	private final int[] rows;
	private final int[] cols;
	private final int[] diagonal;
	
	public Player(String name, Board board){
		this.name = name;
		this.board = board;
		this.rows = new int[board.getRows()];
		this.cols = new int[board.getCols()];
		this.diagonal = new int[2];
	}

	@Override
	public String toString() {
		return name;
	}

	public void takePosition(int row, int col) throws WinnerException {
		board.setOnwer(this, row, col);

		if(++rows[row] == board.totalPositions()){
			throw new WinnerException("Game winner is player " + this + " taken complete row " + row );
		}
		if(++cols[col] == board.totalPositions()){
			throw new WinnerException("Game winner is player " + this + " taken complete column " + row );		
		}
		if(row == col){
			if(++diagonal[0] == board.totalPositions()){
				throw new WinnerException("Game winner is player " + this + " taken complete diagonal left");
			}
		}
		if(row + col + 1 == board.totalPositions()){
			if(++diagonal[1] == board.totalPositions()){
				throw new WinnerException("Game winner is player " + this + " taken complete diagonal right");
			}
		}

	}
		
}