Java Multidimensional Arrays
Arrays within arrays for storing data in rows and columns
🏢 What are Multidimensional Arrays?
Multidimensional arrays are arrays of arrays, creating a table-like structure with rows and columns. Think of them as spreadsheets where you can store data in a grid format, perfect for matrices, game boards, or tables.
// 2D array - like a table with 2 rows and 3 columns
int[][] matrix = {
{1, 2, 3},
{4, 5, 6}
};
System.out.println("Element at row 0, column 1: " + matrix[0][1]);
Output:
Element at row 0, column 1: 2
2D Array Structure
Rows
Horizontal lines of data
matrix[0] // first rowColumns
Vertical lines of data
matrix[0][1] // column 1Access
Use two indices [row][column]
arr[i][j]Dimensions
Can have 2D, 3D, or more
int[][][] cube;🔹 Creating 2D Arrays
Different ways to create and initialize 2D arrays:
🔸 Method 1: Direct Initialization
// Create a 2x3 array (2 rows, 3 columns)
int[][] scores = {
{85, 90, 78}, // Row 0: Student 1's scores
{92, 88, 95} // Row 1: Student 2's scores
};
System.out.println("Student 1, Test 2: " + scores[0][1]);
System.out.println("Student 2, Test 3: " + scores[1][2]);Output:
Student 1, Test 2: 90 Student 2, Test 3: 95
🔸 Method 2: Declare Then Fill
// Create empty 2D array
int[][] grid = new int[2][3]; // 2 rows, 3 columns
// Fill the array
grid[0][0] = 10; grid[0][1] = 20; grid[0][2] = 30;
grid[1][0] = 40; grid[1][1] = 50; grid[1][2] = 60;
System.out.println("Grid filled:");
System.out.println("Top-left: " + grid[0][0]);
System.out.println("Bottom-right: " + grid[1][2]);Output:
Grid filled: Top-left: 10 Bottom-right: 60
🔹 Accessing 2D Array Elements
Use two indices: first for row, second for column:
String[][] classroom = {
{"Alice", "Bob", "Charlie"},
{"Diana", "Eve", "Frank"},
{"Grace", "Henry", "Ivy"}
};
// Access specific students
System.out.println("Front row, middle seat: " + classroom[0][1]);
System.out.println("Back row, left seat: " + classroom[2][0]);
// Get array dimensions
System.out.println("Number of rows: " + classroom.length);
System.out.println("Number of columns: " + classroom[0].length);Output:
Front row, middle seat: Bob Back row, left seat: Grace Number of rows: 3 Number of columns: 3
🔹 Looping Through 2D Arrays
Use nested loops to process all elements:
🔸 Nested For Loops
int[][] multiplication = {
{1, 2, 3},
{2, 4, 6},
{3, 6, 9}
};
System.out.println("Multiplication table:");
for (int row = 0; row < multiplication.length; row++) {
for (int col = 0; col < multiplication[row].length; col++) {
System.out.print(multiplication[row][col] + " ");
}
System.out.println(); // New line after each row
}Output:
Multiplication table: 1 2 3 2 4 6 3 6 9
🔸 Enhanced For Loops
String[][] fruits = {
{"apple", "banana"},
{"orange", "grape"},
{"kiwi", "mango"}
};
System.out.println("All fruits:");
for (String[] row : fruits) {
for (String fruit : row) {
System.out.println("- " + fruit);
}
}Output:
All fruits: - apple - banana - orange - grape - kiwi - mango
🔹 Practical Examples
🔸 Tic-Tac-Toe Board
char[][] board = {
{'X', 'O', 'X'},
{'O', 'X', 'O'},
{'X', 'O', 'X'}
};
System.out.println("Tic-Tac-Toe Board:");
for (int i = 0; i < board.length; i++) {
for (int j = 0; j < board[i].length; j++) {
System.out.print(board[i][j] + " ");
}
System.out.println();
}Output:
Tic-Tac-Toe Board: X O X O X O X O X
🔸 Grade Calculator
// Grades for 3 students, 4 tests each
int[][] grades = {
{85, 90, 78, 92}, // Student 1
{88, 85, 90, 87}, // Student 2
{92, 95, 89, 94} // Student 3
};
System.out.println("Student averages:");
for (int student = 0; student < grades.length; student++) {
int sum = 0;
for (int test = 0; test < grades[student].length; test++) {
sum += grades[student][test];
}
double average = (double) sum / grades[student].length;
System.out.println("Student " + (student + 1) + ": " +
String.format("%.1f", average));
}Output:
Student averages: Student 1: 86.3 Student 2: 87.5 Student 3: 92.5
🔹 3D Arrays (Brief Introduction)
Arrays can have more than 2 dimensions:
// 3D array: 2 floors, 3 rows, 4 columns
int[][][] building = new int[2][3][4];
// Set a value: Floor 0, Row 1, Column 2
building[0][1][2] = 100;
System.out.println("Value at floor 0, row 1, column 2: " +
building[0][1][2]);
// Example: RGB color values for a 2x2 image
int[][][] image = {
{ {255,0,0}, {0,255,0} }, // Row 1: Red, Green
{ {0,0,255}, {255,255,0} } // Row 2: Blue, Yellow
};
System.out.println("Top-left pixel (Red): " +
image[0][0][0] + "," + image[0][0][1] + "," + image[0][0][2]);Output:
Value at floor 0, row 1, column 2: 100 Top-left pixel (Red): 255,0,0