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];
.