Tic_Tac_Toe.java

// A simple program to demonstrate 
// Tic-Tac-Toe Game.

import java.util.*;

public class Tic_Tac_Toe {

	static String[] board;
	static String turn;

	// CheckWinner method will
	// decide the combination
	// of three box given below.
		static String checkWinner() {
			for (int a = 0; a < 8; a++) {
				String line = null;

				switch (a) {
				case 0:
					line = board[0] + board[1] + board[2];
					break;
				case 1:
					line = board[3] + board[4] + board[5];
					break;
				case 2:
					line = board[6] + board[7] + board[8];
					break;
				case 3:
					line = board[0] + board[3] + board[6];
					break;
				case 4:
					line = board[1] + board[4] + board[7];
					break;
				case 5:
					line = board[2] + board[5] + board[8];
					break;
				case 6:
					line = board[0] + board[4] + board[8];
					break;
				case 7:
					line = board[2] + board[4] + board[6];
					break;
				}
				// For X winner
				if (line.equals("XXX")) {
					return "X";
				}

				// For O winner
				else if (line.equals("OOO")) {
					return "O";
				}
			}

			for (int a = 0; a < 9; a++) {
				if (Arrays.asList(board).contains(String.valueOf(a + 1))) {
					break;
				} else if (a == 8) {
					return "draw";
				}
			}

			// To enter the X Or O at the exact place on board.
			System.out.println(turn + "'s turn; enter a slot number to place " + turn + " in:");
			return null;
		}

		// To print out the board.
		/*
		 * |---|---|---| | 1 | 2 | 3 | |-----------| | 4 | 5 | 6 | |-----------| | 7 | 8
		 * | 9 | |---|---|---|
		 */

		static void printBoard() {
			System.out.println("|---|---|---|");
			System.out.println("| " + board[0] + " | " + board[1] + " | " + board[2] + " |");
			System.out.println("|-----------|");
			System.out.println("| " + board[3] + " | " + board[4] + " | " + board[5] + " |");
			System.out.println("|-----------|");
			System.out.println("| " + board[6] + " | " + board[7] + " | " + board[8] + " |");
			System.out.println("|---|---|---|");
		}

		public static void main(String[] args) {
			Scanner in = new Scanner(System.in);
			board = new String[9];
			turn = "X";
			String winner = null;

			for (int a = 0; a < 9; a++) {
				board[a] = String.valueOf(a + 1);
			}

			System.out.println("Welcome to 3x3 Tic Tac Toe.");
			printBoard();

			System.out.println("X will play first. Enter a slot number to place X in:");

			while (winner == null) {
				int numInput;

				// Exception handling.
				// numInput will take input from user like from 1 to 9.
				// If it is not in range from 1 to 9.
				// then it will show you an error "Invalid input."
				try {
					numInput = in.nextInt();
					if (!(numInput > 0 && numInput <= 9)) {
						System.out.println("Invalid input; re-enter slot number:");
						continue;
					}
				} catch (InputMismatchException e) {
					System.out.println("Invalid input; re-enter slot number:");
					continue;
				}

				// This game has two player x and O.
				// Here is the logic to decide the turn.
				if (board[numInput - 1].equals(String.valueOf(numInput))) {
					board[numInput - 1] = turn;

					if (turn.equals("X")) {
						turn = "O";
					} else {
						turn = "X";
					}

					printBoard();
					winner = checkWinner();
				} else {
					System.out.println("Slot already taken; re-enter slot number:");
				}
			}

			// If no one win or lose from both player x and O.
			// then here is the logic to print "draw".
			if (winner.equalsIgnoreCase("draw")) {
				System.out.println("It's a draw! Thanks for playing.");
			}

			// For winner -to display Congratulations! message.
			else {
				System.out.println("Congratulations! " + winner + "'s have won! Thanks for playing.");
			}
		}

	}