Java Arrays

     An array is indexed collection of homogeneous elements.

  v  For storing the similar data type. With single variable name

  v  Once the array is created it is not possible for increase or decrease the size based on the requirement

 v  Arrays shows wonderful performance compared to collections

  Creating an array:

        Syntax:

          {data type}[]  identifier=new {data type}[index];

           Ex: int[] i=new int[10];

                 int[][] j=new int[2][3]; //multi-dimensional array

                 int[][][] k=new int[2][3][2]; //multi-dimensional array

Memory allocation for[2][3] Array:

Array creation having two steps:

Step 1: Declaration

        This declaration is specifies the dimension of an array

        Example:

Important point: At the time of array declaration we are not allowed to specify the size.             int [] a; (or) int a[];

Step 2: Construction

       At the time of array construction we should specify the size

Example:

           int [] a=new int[10]; 

 

Important points:

1.       It is legal to have array size is zero

2.       We are not supposed to give –ve value as array size. It won’t create any compilation error. But it gives runtime error

3.       Arrays always expect integral values as a size. It will allow int, byte, short, char

4.       For knowing the size of array we will use ‘length’ property

Array example:

 class ArrayDemo

{

  public static void main(String[] args)

  {     

        int []a=new int[10];

        //knowing the size of an array

        System.out.println("size of array a: "+ a.length);

        //inserting values

       for(int i=0;i<10;i++){

           a[i]=i;

           System.out.println("Value inserted "+"a["+i+"]");

        }

       // reading the values from array

        for(int j=0;j<10;j++){

            System.out.println("value of a["+j+"] index is:"+a[j]);

        }

  }// end of main method

}//end of class

Output:

size of array a: 10

Value inserted a[0]

Value inserted a[1]

Value inserted a[2]

Value inserted a[3]

Value inserted a[4]

Value inserted a[5]

Value inserted a[6]

Value inserted a[7]

Value inserted a[8]

Value inserted a[9]

value of a[0] index is:0

value of a[1] index is:1

value of a[2] index is:2

value of a[3] index is:3

value of a[4] index is:4

value of a[5] index is:5

value of a[6] index is:6

value of a[7] index is:7

value of a[8] index is:8

value of a[9] index is:9