What is an array?

An array is a very common type of data structure.

• All of the elements sored in the array must be of the same data type.
• Once defined, the size of an array is fixed and cannot increase to accommodate more elements.
• The first element of an array starts with zero.

Instead of entering each piece of data separately:

x0=0; x1=1; x2=2; x3=3; x4=4; etc.

the array x[] will hold data in this way:

x[0]=0; x[1]=1; x[2]=2; x[3]=3; x[4]=4; etc

The index (the number in the bracket[]) can be referenced by a variable for easy looping.

for(count=0; count<5; count++) { System.out.println(x[count]); }

Using an array

To use an array in a program you have to complete all of the following steps:

• Declaring the Array

The syntax for declaring array variables:

<elementType>[] <arrayName>; or <elementType> <arrayName>[]; ----------------------------------------------------- Example that defines that intArray is an ARRAY variable of which will store integer values: int intArray[]; OR int []intArray;

• Constructing the Array

The syntax for constructing an Array:

<arrayName> = new <elementType>[<noOfElements>]; ------------------------------------------------------ Example that intArray will store 10 integer values: intArray = new int[10];

• Initializing the Array

The syntax for initializing an Array:

intArray[0]=1; // Assigns an integer value 1 to the first element 0 of the array intArray[1]=2; // Assigns an integer value 2 to the second element 1 of the array

You can combine steps:

• Syntax for declaration and construction combined:

int intArray[] = new int[10];

• Syntax for declaring and initializing an array

<elementType>[] <arayName> = {<arrayInitializerCode>}; Example that initilializes an integer array of length 4 where the first element is 1 , second element is 2 etc. int intArray[] = {1, 2, 3, 4};

Multidimensional arrays

Multidimensional arrays, are arrays of arrays.

To declare and construct a multidimensional array variable you need to specify each additional index using another set of square brackets.

For example:

int twoD[ ][ ] = new int[4][5] ;

When you allocate memory for a multidimensional array, you need only specify the memory for the first (leftmost) dimension.
You can allocate the remaining dimensions separately.

In Java the length of each array in a multidimensional array is under your control.

For example:

int twoD[][] = new int[4][];

We have four set for the first array (0,1,2,3) - each of those can then be set as housing different numbers of data elements.

twoD[0] = new int[5];
twoD[1] = new int[6];
twoD[2] = new int[7];
twoD[3] = new int[8];

An array of Objects

It is possible to declare array of reference variables.

Syntax:

Class <array_name> = new Class[array_length]

This page extracted facts about arrays from a Java tutorial hub.com tutorial. I suggest you take a look at this site. It is a free educational site.