2D Arrays (Matrices or Grids)

Imagine a video game company contacts you to build Tic-Tac-Toe game. As part of the game development process, you'd need to figure out a method of storing each player's turn. How would we achieve this? Java has a two-dimensional array data structure that we can use. 2D Arrays, also known as Matrices or Grids, can are essentially an "array of arrays."

Creating 2D Arrays

To create a 2D Array, we would use: type[][] name = new type[rows][columns];

Here are some examples:

// Create a 2x4 grid of doubles
double[][] doubleGrid = new double[2][4];

// Create a 5x6 grid of Strings
String[][] stringGrid = new String[5][6];

// Create a 6x10 grid of chars
char[][] charGrid = new char[6][10];

// Create a 3x3 grid of integers
int[][] intGrid = new int[3][3];

// Initializing our Tic-Tac-Toe Grid with X's (1's) as the winner.
int[][] gameBoard = {
  {1, 0, 2},
  {0, 1, 2},
  {0, 0, 1}
 };

What 2D Arrays Look Like

If you were to visualize a 2D Array, it would be easiest to think of it like a table of values:

Here is what a 3x3, 2D Array would look like:

row/col	0	1	2
0	(0, 0)	(1, 0)	(2, 0)
1	(0, 1)	(1, 1)	(2, 1)
2	(0, 2)	(1, 2)	(2, 2)

Where the top and far left rows represent our X and Y indexes.

Utilizing 2D Arrays

Now that we understand what 2D Arrays look like, and how to create them, we can focus on utilization.

Let's say we have a 3x3 grid, named gameBoard, with the value of our Tic-Tac-Toe game. In this case, 0 represents a blank space, 1 represents a X, and 2 represents an O.

Here is what our grid looks like with X as the winner:

row/col	0	1	2
0	1	0	2
1	0	1	0
2	2	2	1

Getting an Element:

Let's say we want to access a specific element of our grid. For this, we use: int elem = grid[row][col];. With that said, we want to grab the element in the middle of the grid. So we would use: int elem = gameBoard[1][1];, which would give us a 1. Now, we want to get the element in the top right corner of the canvas. In this case, we use: int elem = gameBoard[2][0]; and we get 2.

Setting an Element:

In order to set an element of a grid we use: grid[row][col] = elem;. If we wanted to make O the winner of our game we would have to set the elements at (0, 0) and (0, 1) to 2. In order to do this we would use:

gameBoard[0][0] = 2; 
gameBoard[0][1] = 2;

Now our Grid looks like:

row/col	0	1	2
0	2	0	2
1	2	1	0
2	2	2	1

Getting a Row:

Finally, to get a specific row of a grid, we use int[] row = grid[row];. If were were to access the values in the 2nd row of our board, we would use int[] 2ndRow = gameBoard[1];.