Creation of 2D Array

// Declare a 2D array
int[][] array = new int[3][4]; // 3 rows and 4 columns

// Declare and initialize with values
int[][] array = {
    {1, 2, 3},
    {4, 5, 6},
    {7, 8, 9}
};

Indexing 2D Arrays

To index a 2D array, place the row number, followed by the column number.

// Access elements in the array
int value = array[0][1]; // Gets the number in the 1st row and 2nd column
System.out.println(value); // Output: 2

int value2 = array[1][2]; // Gets the number in the 2nd row and 3rd column
System.out.println(value2); // Output: 6

// Whoopsie daisies! Error! This is out of bounds
int value3 = array[20][10];
System.out.println(value3);

Iteration of 2D Array

To iterate through a 2D array:

Row-major order

// For loop: Add 5 to all elements of the array
for (int row = 0; row < array.length; row++) {
    for (int col = 0; col < array[row].length; col++) {
        array[row][col] += 5; // Add 5 to each element
    }
}

// Foreach loop: Output all elements of the array
for (int[] row : array) {
    for (int item : row) {
        System.out.print(item + " ");
    }
    System.out.println(); // Adds a newline after each row
}

Column-major order

for (int col = 0; col < array[0].length; col++) {
    for (int row = 0; row < array.length; row++) {
        System.out.print(array[row][col]);
    }
    System.out.println();
}

Example - 2020 FRQ Part 4

public class Seat {
    private boolean available;
    private int tier;

    public Seat(boolean isAvail, int tierNum) {
        available = isAvail;
        tier = tierNum;
    }

    public boolean isAvailable() {
        return available;
    }

    public int getTier() {
        return tier;
    }

    public void setAvailability(boolean isAvail) {
        available = isAvail;
    }
}

public class Theater {
    private Seat[][] theaterSeats;

    public Theater(int seatsPerRow, int tier1Rows, int tier2Rows) {
        this.theaterSeats = new Seat[tier1Rows + tier2Rows][seatsPerRow];
    }

    public boolean reassignSeat(int fromRow, int fromCol, int toRow, int toCol) {
        Seat fromSeat = theaterSeats[fromRow][fromCol];
        Seat toSeat = theaterSeats[toRow][toCol];

        if (fromSeat.getTier() < toSeat.getTier() || !toSeat.isAvailable()) {
            return false;
        }

        theaterSeats[fromRow][fromCol] = toSeat;
        theaterSeats[toRow][toCol] = fromSeat;
        return true;
    }
}