Two dimensional Array - How to represent two-dimensional (2D) data ( table / grid ) in Java?

1. Introduction

Every element in the data set has two parameters / properties. Examples of day to day two-dimensional data strutures include a table, a grid, a martix etc.

1.1. Example

For ease of understanding lets consider a simple two-dimensional data-set - a table

Here, the two-dimensions of every element in the data-set are the row and column.

2. Using two-dimensional arrays.

2.1. Introduction

"An array is a container object that holds a fixed number of values of a single type. Each item in an array is called an element, and each element is accessed by its numerical index." A two-dimensional array is one where each element is accessed by its two numerical indices.

The first step in using arrays is the initialisation bit. An important point to note about arrays is that you should specify the size of the array (only the row size is mandatory for 2-d arrays) during initialisation and that this size cannot be changed after array creation.

2.2. Initialisation

int[][] tableData = new int[3][3];

The above code initialises a 2-dimensional int array with 3 rows and 3 columns. An alternate way to initialise a 2-d array if you know its connect before hand is by...

int[][] tableData  = new int[][]
{
    {1, 2, 3}, {3, 1, 2}, {2, 3, 1}
};

2.3. Populating with data

Now lets populate it with the values from the above table.

    	int[][] tableData  = new int[3][3];
 
    	// Row 0 Col 0
    	tableData [0][0] = 1;
    	// Row 0 Col 1
    	tableData [0][1] = 2;
    	// Row 0 Col 2
    	tableData [0][2] = 3;
 
    	// Row 1 Col 0
    	tableData [0][0] = 3;
    	// Row 1 Col 1
    	tableData [0][1] = 1;
    	// Row 1 Col 2
    	tableData [0][2] = 2;
 
    	// Row 2 Col 0
    	tableData [0][0] = 2;
    	// Row 2 Col 1
    	tableData [0][1] = 3;
    	// Row 2 Col 2
    	tableData [0][2] = 1;

2.3. Retrieving data

If you feel it was easy so far, then its get even more easier when it comes to extracting values out of the populated array. To retrieve a value at a given row and column you can just do

int tableValue = twoDArray[1][1];

To retrive all the values from a two-dimensional array your can use a for-loop.

for (int row = 0; row < twoDArray.length; row++)
{
    int[] tableRow = twoDArray[row];
    for (int col = 0; col < tableRow.length; col++)
    {
    		int tableValue = tableRow[col];
    		System.out.println("The table value at row - '" + row + "' col - " + col 
    					+ " is " + tableValue);
    }
}