Java Fundamentals - Arrays

An array is a data structure that represents an index collection of fixed no of homogeneous data

elements.

1.Declaring Arrays

you can type the [] before or after the name, and adding a space is optional. This means that all four of these statements do the exact same thing:

int[] numAnimals;

int [] numAnimals2;

int numAnimals3[];

int numAnimals4 [];

The following are the valid declarations for multidimensional arrays.

int[][] a;

int a[][];

int [][]a;

int[] a[];

int[] []a;

we can specify the dimension before name of variable also, but this facility is available only for the first variable.

int[] a[],b[];

int[] []a,[]b; //Wrong

2.Construction of Arrays

Single Dimension : Arrays are internally implemented as object hence by using new operator we can construct an array.

Compulsory at the time of construction we should specify the size otherwise compile time error.

int[] a = new int[10]; _/

int[] a = new int[]; X C.E

It is legal to have an error with size 0 there is no C.E or R.E

int[] a = new int[0];

If we are specifying array size with some –ve integer, we will get R.E:NegativeArraySizeException.

int[] a = new int[-10];

The only allowed Data type to allow the size are byte, short, char, int. if we are using any other datatype we will get a C.E.

int[] a = new int[10];

int[] a1 = new int[10l];

int[] a = new int[10L]; --> C.E possible loss of precision found: long required: int

Multi Dimension: In java multidimensional arrays are implemented as single dimension arrays. This approach improves performance with respect to memory.

int[][] a = new int[3][2];

int[][] a = new int[4][]

a[0] = new int[1];

a[1] = new int[2];

a[2] = new int[4];

a[3] = new int[3];

declare an array for the following diagram

a[][][] = new int[2][][];

a[0]    = new int[3];

a[0][1] = new int[1];

a[0][2] = new int[2];

a[0][3] = new int[3];

a[1]    = new int[2][2];

3.Initialization of arrays

Once we created an array all it’s elements initialized with default values.

int[] a = new int[3];

System.out.println(a[0]); O/P: 0

System.out.println(a); O/P: [I@10b62c9

int[][] a = new int[3][2];

System.out.println(a); --> [I@10b62c9

System.out.println(a[0]); --> [[I@82ba41

System.out.println(a[0][0]); --> 0

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

System.out.println(a); --> [I@10b62c9

System.out.println(a[0]); --> null

System.out.println(a[0][0]); --> NullPointerException

4.Declaration and Initialization Array in a single line

int[] a = {10,20,30};

String[] s = {“Chiru”,”Allu”,”Ram”,”Akil”}

5.length Vs length();

length: It is the final variable applicable for array objects. It represents the size of the array.

int [] a = new int[5];

System.out.println(a.length()); --> C.E

System.out.println(a.length); --> 6

length():It is the final method applicable only for String Objects. Ex:

String s = "raju";

System.out.println(s.length); --> C.E

System.out.println(s.length()); --> 4

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