Tic-Tac-Toe Game in Java

Tic-Tac-Toe is a classic game that two people can enjoy together. It is played on a 3x3 grid where players take turns placing their marks, X or O, in empty spots. The main goal is to get three of the same marks in a row-horizontally, vertically, or diagonally.

We are going to build a Java program that lets two players play the Tic-Tac-Toe game right from the console. There will be a board with numbers from 1 to 9, and we have to select a spot. And when it's our turn, we have to choose a number to put the mark there, and the board will update after every move, and the game continues until someone wins or it ends in a tie.

Game Board Layout

The game board layout will look something like this:

      |---|---|---|        
      | 1 | 2 | 3 |
      |-----------|
      | 4 | 5 | 6 |
      |-----------|
      | 7 | 8 | 9 |
      |---|---|---|  

How to Play the Game

The steps to play the game are listed below:

• Both players choose either X or O to mark their cells.
• There will be a 3x3 grid with numbers assigned to each of the 9 cells.
• The player who chooses X begins to play first.
• He enters the cell number where he wishes to place X.
• Now, both O and X play alternatively until one of the two wins.
• Winning criteria: Whenever any of the two players has fully filled one row/ column/ diagonal with their symbol (X/ O), they win and the game ends.
• If neither of the two players wins, the game is said to have ended in a draw.

Sample Input: Enter a slot number to place X in: 3 

Sample Output:

      |---|---|---|        
      | 1 | 2 | X |
      |-----------|
      | 4 | 5 | 6 |
      |-----------|
      | 7 | 8 | 9 |
      |---|---|---|  

Sample Input:

Now, O's turn, Enter a slot number to place O in: 5

Sample Output:

      |---|---|---|        
      | 1 | 2 | X |
      |-----------|
      | 4 | O | 6 |
      |-----------|
      | 7 | 8 | 9 |
      |---|---|---|  

So, like this game will be continued.

Before you begin coding the project, it’s important to understand two key concepts used throughout:

Arrays: Arrays are used to store multiple values in a single variable. In this Tic-Tac-Toe game, we use a 1D array of size 9 to represent the 3x3 board, with each slot initialized to numbers 1–9.

Example:

// Creating a board with 9 positions

String[] board = new String[9];

// Filling the board with slot numbers (1 to 9)

for (int a = 0; a < 9; a++) {

board[a] = String.valueOf(a + 1);

}

Conditionals (if, switch): Conditional statements help the program decide what to do next.

For Example:

• if is used to validate input, check for a winner, or alternate turns.
• switch is used in the checkWinner() method to determine all possible winning combinations.

Examples:

if statement:

// Example of an if condition to validate move

if (board[numInput - 1].equals(String.valueOf(numInput))) {

board[numInput - 1] = turn;

} else {

System.out.println("Slot already taken; re-enter slot number:");

}

switch case:

// Example of a switch statement used to check winning lines

switch (a) {

case 0:

line = board[0] + board[1] + board[2];

break;

case 1:

line = board[3] + board[4] + board[5];

break;

// ... other cases to check rows, columns, and diagonals

}

Project Implementation

// A simple Java program to demonstrate
// Tic-Tac-Toe Game
import java.util.*;

public class Geeks {

    static String[] board;
    static String turn;

    // CheckWinner method will decide the winner
    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";
            }
        }

        System.out.println(turn + "'s turn; enter a slot number to place " + turn + " in:");
        return null;
    }

    // To print the board
    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;

            try {
                numInput = in.nextInt();

                // Check range
                if (!(numInput > 0 && numInput <= 9)) {
                    System.out.println("Invalid input; re-enter slot number:");
                    continue;
                }

                // Check if slot is available
                if (board[numInput - 1].equals(String.valueOf(numInput))) {
                    board[numInput - 1] = turn;

                    // Toggle turn
                    turn = turn.equals("X") ? "O" : "X";

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

            } catch (InputMismatchException e) {
                System.out.println("Invalid input; re-enter slot number:");
                in.nextLine(); // Consume invalid input to prevent infinite loop
            }
        }

        // Final result
        if (winner.equalsIgnoreCase("draw")) {
            System.out.println("It's a draw! Thanks for playing.");
        } else {
            System.out.println("Congratulations! " + winner + "'s have won! Thanks for playing.");
        }

        in.close();
    }
}

Output:

Below is the output of the above program :
Welcome to 3x3 Tic Tac Toe.
|---|---|---|
| 1 | 2 | 3 |
|-----------|
| 4 | 5 | 6 |
|-----------|
| 7 | 8 | 9 |
|---|---|---|
X will play first. Enter a slot number to place X in:
3
|---|---|---|
| 1 | 2 | X |
|-----------|
| 4 | 5 | 6 |
|-----------|
| 7 | 8 | 9 |
|---|---|---|
O's turn; enter a slot number to place O in:
5
|---|---|---|
| 1 | 2 | X |
|-----------|
| 4 | O | 6 |
|-----------|
| 7 | 8 | 9 |
|---|---|---|
X's turn; enter a slot number to place X in:
6
|---|---|---|
| 1 | 2 | X |
|-----------|
| 4 | O | X |
|-----------|
| 7 | 8 | 9 |
|---|---|---|
O's turn; enter a slot number to place O in:
1
|---|---|---|
| O | 2 | X |
|-----------|
| 4 | O | X |
|-----------|
| 7 | 8 | 9 |
|---|---|---|
X's turn; enter a slot number to place X in:
9
|---|---|---|
| O | 2 | X |
|-----------|
| 4 | O | X |
|-----------|
| 7 | 8 | X |
|---|---|---|
Congratulations! X's have won! Thanks for playing.

Steps to Run on IntelliJ IDE

• Open IntelliJ IDE.
• Create a New Java project.
• Right-click on the src folder and create a new class like a class named Geeks.
• Now, write your source code and ctrl+s to save it.
• Now, to execute the program right-click the src folder and click on run as Java application.

You can check below screenshot for your reference.