Advanced Java · Week 1

2D Arrays

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Java 2 Guided Tutorials - Week 1: 2D Arrays

What You'll Learn

Welcome to Week 1 of Java 2! This week, we'll dive into the world of 2D arrays. We'll start with a quick review of 1D arrays from Java 1, then move on to understanding and working with 2D arrays.

                    Lesson Overview:
                    Review of 1D arrays from Java 1
Introduction to 2D arrays
Declaring and initializing 2D arrays
Accessing and modifying elements in 2D arrays
Common operations with 2D arrays
Quiz to test your knowledge
Weekly project to apply what you've learned

                

By the end of this week, you'll have a solid understanding of 2D arrays and be able to use them in your Java programs. Let's get started!

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:

// 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

Try it Yourself

Create a 1D array of your favorite fruits and print them out using a for-each loop. Use the compiler below to write and run your code, then paste the output in the autograder to check your work.

Write your code here

Make it print Apple Banana Orange

Did it work?

Your program should print this:

Apple Banana Orange

Paste what you got:

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.

                    Key Points:
                    2D arrays are useful for representing grids, matrices, or tables
They are declared using two sets of square brackets
The first index represents the row, the second represents the column

                

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

// 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;

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.

Write your code here

Make it print X O X O X O X O

Did it work?

Your program should print this:

X O X
O X O
X   O

Paste what you got:

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].

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
}

Try it Yourself

Create a 3x3 2D array representing student grades for three subjects. Calculate and print the average grade for each student.

Write your code here

Make it print Student 1 average: 85.0 Student 2 average: 78.33 Student 3 average: 92.67

Did it work?

Your program should print this:

Student 1 average: 85.0
Student 2 average: 78.33
Student 3 average: 92.67

Paste what you got:

4. 2D Arrays Quiz

2. What does the following code print?

int[][] arr = {{1, 2}, {3, 4}, {5, 6}};
System.out.println(arr[1][1]);

3. How many elements are in the following 2D array?

int[][] matrix = new int[3][4];

Quick check

1. How do you declare a 2D array of integers with 3 rows and 4 columns?
2. What does the following code print? int[][] arr = {{1, 2}, {3, 4}, {5, 6}}; System.out.println(arr[1][1]);
3. How many elements are in the following 2D array? int[][] matrix = new int[3][4];

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.

                    Requirements:
                    Create a 3x3 2D array to represent the Tic-Tac-Toe board
Implement a method to print the current state of the board
Allow two players to take turns placing their marks (X and O)
Check for a win condition after each move
End the game when there's a winner or a draw

                

Here's a template to get you started:

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;
    }
}

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.

Write your code here

Make it print Player X wins!

Did it work?

Your program should print this:

Player X wins!

Paste what you got:

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