Arrays

An array is simply a sequence of either objects or primitives that are all the same type and are packaged together under one identifier name. Arrays are defined and used with the square-brackets indexing operator [ ] :

int[] a1;

There are primarily 2 types of Arrays.
1. One Dimensional Array
2. Two Dimensional Array

1. One Dimensional Array

One dimensional array are the arrays which contain only 1 row and many number of columns. like [1,2,3,4,5,6….]

You can also put the square brackets after the identifier to produce exactly the same meaning:

int a1[];
int a2[] = new int[5]; // limit of array is defined as 5

There are situations in which we want to declare an array without mentioning it’s size. In those cases we do this as :

int[] a1 = { 1, 2, 3, 4, 5 };

2. Two Dimensional Array

multidimensional arrays are arrays of arrays. They are formed with Rows and Columns.They are declared as :

int twoDArray[][] = new int[4][5]; // this array contains 4 rows and 5 columns

Jagged Arrays

Jagged arrays are the arrays which are not limited to a particular order. Suppose we want 4 columns in first row, 2 columns in 2nd row and 3 columns in 3rd row. like this will look like this :-

1  2  3  4
1  2   
1  2  3

These types of arrays are handled in java special syntax. Let’s review a program that demonstrate the arrays functionality

public class JavaArrays {
	public static void main(String[] args) {
		// 1 Dimensional Array
		int arr1[] = { 1, 2, 3, 4, 5, 6 }; // 1 dimensional array
		for (int i = 0; i < 6; i++)
			System.out.println(arr1[i]); // printing array values

		// 2 Dimensional Array
		int arr2[][] = new int[2][3]; // dimensional array of 2 rows and 3
										// columns, all elements will be
										// initialized to 0

		for (int row = 0; row < 2; row++)
			// loop for iterating through array rows
			for (int col = 0; col < 3; col++)
				// loop for iterating through array columns
				System.out.println(arr2[row][col]); // printing array value

		// Jagged Arrays
		int arr3[][] = new int[3][5];
		arr3[0] = new int[4]; // four columns assigned to 1st row
		arr3[1] = new int[2]; // two columns assigned to 2nd row
		arr3[2] = new int[3]; // three columns assigned to 3rd row

		for (int row = 0; row < 3; row++) {
			for (int col = 0; col < arr3[row].length; col++) {
				arr3[row][col] = 200; // assign arbitrary value to each element
										// of jagged array
			}
		}

		// printing Jagged arrays value
		for (int row = 0; row < 3; row++) {
			for (int col = 0; col < arr3[row].length; col++) {
				System.out.print(" " + arr3[row][col]);
			}
			System.out.println(); // to output a blank line
		}
	}
}