Dots and Boxes Game Java Source code

Dots and Boxes, also known as the "Dot Game" or "Squares," is a classic pen-and-paper game that has been enjoyed by people of all ages for decades. In this article, we'll walk you through the process of creating a Dots and Boxes game in Java from scratch. By the end of this section, we have a complete Java source code for the game.

Prerequisites

Before we dive into the code, make sure you have the following prerequisites:
Java Development Kit (JDK) installed on your computer.
A code editor (e.g., Eclipse, IntelliJ IDEA, or Visual Studio Code).

Understanding the Rules

In Dots and Boxes, two players take turns connecting dots on a grid of dots to form squares. When a player completes a square, they score a point and get another turn. The game ends when all possible lines are drawn, and the player with the most squares wins.

DotsAndBoxes.java

import java.util.Scanner;
public class DotsAndBoxes {
    private char[][] grid;
    private char currentPlayer;
    private int playerXScore;
    private int playerOScore;
    public DotsAndBoxes() {
        grid = new char[4][4];
        currentPlayer = 'X';
        playerXScore = 0;
        playerOScore = 0;
        initializeGrid();
    }
    private void initializeGrid() {
        for (int i = 1; i <= 3; i++) {
            for (int j = 1; j <= 3; j++) {
                grid[i][j] = ' ';
            }
        }
    }
    private void displayGrid() {
        for (int i = 1; i <= 3; i++) {
            for (int j = 1; j <= 3; j++) {
                System.out.print(grid[i][j]);
                if (j < 3) {
                    System.out.print(" | ");
                }
            }
            System.out.println();
            if (i < 3) {
                System.out.println("---------");
            }
        }
    }
    private boolean isValidMove(int row, int col) {
        return row >= 1 && row <= 3 && col >= 1 && col <= 3 && grid[row][col] == ' ';
    }
    private void makeMove(int row, int col) {
        grid[row][col] = currentPlayer;
    }
    private boolean isBoxCompleted(int row, int col) {
        return (row > 1 && grid[row - 1][col] != ' ' && grid[row - 1][col] != '|' &&
                row < 3 && grid[row + 1][col] != ' ' && grid[row + 1][col] != '|' &&
                col > 1 && grid[row][col - 1] != '-' && grid[row][col - 1] != ' ' &&
                col < 3 && grid[row][col + 1] != '-' && grid[row][col + 1] != ' ');
    }
    private boolean checkForWinner() {
        for (int i = 1; i <= 3; i++) {
            if (grid[i][1] != ' ' && grid[i][1] == grid[i][2] && grid[i][2] == grid[i][3]) {
                return true; // Check rows
            }
            if (grid[1][i] != ' ' && grid[1][i] == grid[2][i] && grid[2][i] == grid[3][i]) {
                return true; // Check columns
            }
        }
        if (grid[1][1] != ' ' && grid[1][1] == grid[2][2] && grid[2][2] == grid[3][3]) {
            return true; // Check diagonal from top-left to bottom-right
        }
        if (grid[1][3] != ' ' && grid[1][3] == grid[2][2] && grid[2][2] == grid[3][1]) {
            return true; // Check diagonal from top-right to bottom-left
        }
        return false;
    }
    private void switchPlayer() {
        currentPlayer = (currentPlayer == 'X') ? 'O' : 'X';
    }
    private boolean isGameOver() {
        return checkForWinner();
    }
    private void displayWinner() {
        System.out.println("Game Over!");
        System.out.println("Player " + currentPlayer + " wins!");
    }
    public void playGame() {
        Scanner scanner = new Scanner(System.in);
        while (true) {
            displayGrid();
            System.out.println("Player " + currentPlayer + "'s turn");
            System.out.print("Enter row (1-3): ");
            int row = scanner.nextInt();
            System.out.print("Enter column (1-3): ");
            int col = scanner.nextInt();
            if (isValidMove(row, col)) {
                makeMove(row, col);
                if (isBoxCompleted(row, col)) {
                    System.out.println("Player " + currentPlayer + " completed a box!");
                }
                if (checkForWinner() || playerXScore + playerOScore == 9) {
                    break;
                }
                switchPlayer();
            } else {
                System.out.println("Invalid move. Try again.");
            }
        }
        displayGrid();
        displayWinner();
        scanner.close();
    }
    public static void main(String[] args) {
        DotsAndBoxes game = new DotsAndBoxes();
        game.playGame();
    }
}

Output:

  |   |  
---------
  |   |  
---------
  |   |  
Player X's turn
Enter row (1-3): 1
Enter column (1-3): 1
X |   |  
---------
  |   |  
---------
  |   |  
Player O's turn
Enter row (1-3): 2
Enter column (1-3): 1
X |   |  
---------
O |   |  
---------
  |   |  
Player X's turn
Enter row (1-3): 1
Enter column (1-3): 2
X | X |  
---------
O |   |  
---------
  |   |  
Player O's turn
Enter row (1-3): 2
Enter column (1-3): 2
X | X |  
---------
O | O |  
---------
  |   |  
Player X's turn
Enter row (1-3): 1
Enter column (1-3): 3
X | X | X
---------
O | O |  
---------
  |   |  
Game Over!
Player X wins!

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