Basics – Two Dimensional Array in Java

INTRO:

• Click ARRAY to learn about that.
• A 2D array is an array of one-dimensional arrays.
• 2D array is a collection of data cells.
• 2D array is stored in the form of rows and columns and is represented in the form of a matrix.
• We can access it by row index and column index (like an Excel File).

SYNTAX:

dataType [][] arrayName = new dataType[rowSize][columnSize];

2D ARRAY DECLARATION:

int[][] a = new int[4][2]; //4 rows & 2 columns
String[][] name = new String[5][3]; // 5 rows & 3 columns

 int[][] wrong = new int[][]; // not OK, must specify row
 int[][] right = new int[2][]; // OK

• We must specify first dimension (row_size).

TOTAL ELEMENT:

• The total number of elements in this 2-D array is:

number_of_rows * number_of_columns

LAYOUT OF THE ARRAY:

int[ ][ ] a = new int[3][3];

2D ARRAY INITIALIZATION:

Approach 1:

public static void main(String[] args) 
{
//Array initialization
		int arr[][] = {{ 1, 2, 3 },{ 4, 5, 6 },{ 7, 8, 9 }};
	
//Array display	
		for (int i = 0; i < 3; i++) 
		{
			for (int j = 0; j < 3; j++) 
			{
				System.out.print(arr[i][j] + " ");
			}
			System.out.println();
		}
}

Approach 2:

public static void main(String[] args) {

//Array Initialization
		int arr[ ][ ] = new int[3][3];

		arr[0][0] = 1;
		arr[0][1] = 2;
		arr[0][2] = 3;

		arr[1][0] = 4;
		arr[1][1] = 5;
		arr[1][2] = 6;

		arr[2][0] = 7;
		arr[2][1] = 8;
		arr[2][2] = 9;
	
//Array Display	
		for (int i = 0; i < 3; i++) 
		{
			for (int j = 0; j < 3; j++) 
			{
				System.out.print(arr[i][j] + " ");
			}
			System.out.println();
		}
	}

Approach 3:

public static void main(String[] args) {

		int arr[ ][ ] = new int[3][3];

		for (int i = 0; i < 3; i++) 
		{
			for (int j = 0; j < 3; j++) 
			{
				arr[i][j]=i+1;   //Array Initialization
				System.out.print(arr[i][j] + " "); //Display
			}
			System.out.println();
		}
	}

Approach 1 & 2 output:

1 2 3
4 5 6
7 8 9

Approach 3 output:

1 1 1
2 2 2
3 3 3

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LENGTH OF THE 2D ARRAY = NUMBER OF ROWS

	int array1[][] = new int [5][6];
	int array2[][] = new int [3][0];
	int array3[][] = new int [0][];
	int array4[][] = { {1,2,3,4}, {5,6} };
	int array5[][] = { {100}, {10,20,30}, {1,2,3} };
		
	System.out.println("Array1 length: " + array1.length);
	System.out.println("Array2 length: " + array2.length);
	System.out.println("Array3 length: " + array3.length);
	System.out.println("Array4 length: " + array4.length);
	System.out.println("Array5 length: " + array5.length);

Output:

Array1 length: 5
Array2 length: 3
Array3 length: 0
Array4 length: 2
Array5 length: 3

NOTE:

• Must provide row size in array declaration.
• Row size can be zero.
• Column size may or may not mention in array declaration.
• Row & column size must be positive integer.

array_name.length    //returns row length
array_name[0].length //returns column length

Ex 1: Find row & column length

        int array1[][] = new int [5][6];
		int array2[][] = new int [3][0];
		int array3[][] = new int [1][1];
		int array4[][] = { {1,2,3,4}, {5,6} };
		int array5[][] = { {100}, {10,20,30}, {1,2,3,5,6,8,9} 
		
		System.out.println("Array1 row length: " + array1.length);
		System.out.println("Array1 column length: " + array1[0].length);
		
		System.out.println("Array2 row length: " + array2.length);
		System.out.println("Array2 column length: " + array2[0].length);
		
		System.out.println("Array3 row length: " + array3.length);
		System.out.println("Array3 column length: " + array3[0].length);
		
		System.out.println("Array4 row length: " + array4.length);
		System.out.println("Array4 column1 length: " + array4[0].length);
		System.out.println("Array4 column2 length: " + array4[1].length);
		
		System.out.println("Array5 row length: " + array5.length);
		System.out.println("Array5 column1 length: " + array5[0].length);
		System.out.println("Array5 column2 length: " + array5[1].length);
		System.out.println("Array5 column3 length: " + array5[2].length);

OUTPUT:

Array1 row length: 5
Array1 column length: 6
Array2 row length: 3
Array2 column length: 0
Array3 row length: 1
Array3 column length: 1
Array4 row length: 2
Array4 column1 length: 4
Array4 column2 length: 2
Array5 row length: 3
Array5 column1 length: 1
Array5 column2 length: 3
Array5 column3 length: 7

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BASIC PROGRAMS IN 2D ARRAY:

Ex 1: Basic Addition between two arrays

public class Practice {

	public static void main(String[] args) 
	{
		int array1[][] = { {10,22,33,44}, {11,20,40,5} };
		int array2[][] = { {9,12,3,4}, {17,28,49,50} };
		int sumArray[][] = new int[2][4];
		int rows, columns;

		for(rows=0;rows<array1.length;rows++)
		{
			for(columns=0;columns<array1[0].length;columns++)
			{
			sumArray[rows][columns] = array1[rows][columns] + array2[rows][columns];
			}
		}
		
		System.out.println("Sum values");
		for(rows=0;rows<array1.length;rows++)
		{
			for(columns=0;columns<array1[0].length;columns++)
			{
				System.out.print(sumArray[rows][columns] + " ");
			}
			System.out.println();
		}				
	}
}

Output:

Sum values
19 34 36 48
28 48 89 55

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