ARRAY

  

   Array is a group of contiguous or related data items that share a commonname.

   One Dimensional Array:

o   A list of items can be given one variable name using only one subscript and such a variable is called a single-subscripted variable or a one-dimensional array.

o   Creation of array involves three steps:

a)    Declaring the array: In Java array may be declared in two forms:

type arrayname[];

type [] arrayname;

Ex:   int num1[];

         float[] num2;

        

b)    Creationof Array: After declaring an array, we need to create it in the memory. In Java new operator is used to create an array:

arrayname=new type[size];

Ex:  num1=new int[5];

         num2=new float[10];

The above two steps can be combined into single step as follows:

         int num=new int[5]; 

c)     Initialization of Arrays:There are various ways to initialize an array:

Arrayname[subscript]=value;

Ex:num[0]=10;

         num[1]=20;

It is also possible to initialize an array at the time of declaration:

type  arrayname[]={list of values};

Ex: int num[]={10,20,30,40};

It is also possible to assign an array object to another:

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

int b[];

b=a;

Loops can also be used to initialize an array:

int num[50];

for(int i=0;i<50;i++)

     num[i]=0;

d)    Array Length:In Java length is used to calculate the length of an array:

Ex: int size=num.length;

Usefulwhen the size of array is not known.

   Two Dimensional Array:

o   Declaring 2D array:int num[][];

o   Creating memory for 2D array:num=new int[3][4];

int num[][]=new int[3][4];

o   Initializing 2D array:

int num[2][3]={0,0,0,1,1,1};

int num[2][3]={{0,0,0},{1,1,1}};

int num[2][3]={

{0,0,0},

{1,1,1}

      };

o   Accessing Values: Values from 2D array can be accessed using subscript or index value:

int val=num[1][2];

    Variable Size Array:

o   Java treats multidimensional array as “arrays of arrays”. It is possible to declare a two dimensional array as follows:

int x[][]=new int[3][];

x[0]=new int[2];

x[1]=new int[4];

x[2]=new int[3];

o   Each row of the array x have different length.