2D Arrays

1. Review of 1D Arrays

Quick Recap: 1D Arrays

Before we dive into 2D arrays, let's quickly review 1D arrays from Java 1:

• An array is a collection of elements of the same data type
• Arrays have a fixed size once created
• Array indices start at 0

Here's a quick example of creating and using a 1D array:

<code>// Declaring and initializing an array
int[] numbers = {1, 2, 3, 4, 5};

// Accessing elements
System.out.println(numbers[0]); // Outputs: 1

// Modifying elements
numbers[2] = 10;

// Iterating through an array
for (int i = 0; i < numbers.length; i++) {
    System.out.print(numbers[i] + " ");
}
// Outputs: 1 2 10 4 5</code>

2. Introduction to 2D Arrays

What are 2D Arrays?

A 2D array is an array of arrays. You can think of it as a table with rows and columns. Each element in a 2D array is accessed using two indices: one for the row and one for the column.

Here's how to declare and initialize a 2D array:

<code>// Method 1: Declare and initialize in one line
int[][] matrix = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};

// Method 2: Declare first, then initialize
int[][] grid = new int[3][3];
grid[0][0] = 1; grid[0][1] = 2; grid[0][2] = 3;
grid[1][0] = 4; grid[1][1] = 5; grid[1][2] = 6;
grid[2][0] = 7; grid[2][1] = 8; grid[2][2] = 9;</code>

Try creating a 2D array representing a tic-tac-toe board. Use 'X', 'O', and ' ' (space) as elements. Print out the board using nested loops.

3. Accessing and Modifying 2D Arrays

Working with 2D Arrays

To access or modify elements in a 2D array, we use two indices: [row][column].

<code>int[][] matrix = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};

// Accessing elements
System.out.println(matrix[1][2]); // Outputs: 6

// Modifying elements
matrix[0][1] = 10;

// Iterating through a 2D array
for (int i = 0; i < matrix.length; i++) {
    for (int j = 0; j < matrix[i].length; j++) {
        System.out.print(matrix[i][j] + " ");
    }
    System.out.println(); // New line after each row
}</code>

4. 2D Arrays Quiz

5. Weekly Project: Tic-Tac-Toe Game

Project Description

For this week's project, you'll create a simple Tic-Tac-Toe game using a 2D array to represent the game board.

Here's a template to get you started:

<code>import java.util.Scanner;

public class TicTacToe {
    private static char[][] board = new char[3][3];
    private static char currentPlayer = 'X';

    public static void main(String[] args) {
        initializeBoard();
        playGame();
    }

    private static void initializeBoard() {
        // Initialize the board with empty spaces
    }

    private static void printBoard() {
        // Print the current state of the board
    }

    private static void playGame() {
        // Implement the game logic here
    }

    private static boolean checkWin() {
        // Check for a win condition
        return false;
    }

    private static boolean isBoardFull() {
        // Check if the board is full (draw condition)
        return false;
    }
}
</code>

Implement the missing methods and game logic. Use the online compiler to write and test your code. Once you're satisfied with your program, paste the output of a complete game in the autograder to check your work.