Array: One dimensional Array

An array is a container object that holds a fixed number of values of a single type. Thelength of an array is established when the array is created. After creation, its length is fixed.

Each item in an array is called an element, and each element is accessed by itsnumerical index. Numbering begins with 0. The 9th element, for example, would thereforebe accessed at index 8.

An array of 10 elements

Declaring a Variable to Refer to an array:

datatype[ ] arrayName; ordatatype [ ]arrayName; ordatatype arrayName[];For example to declare an array of integer variables:int[ ] a; orint [ ]a; orint a[ ]; this form is discouraged, please don’t use thisalways use the first form i.e. datatype[ ] arrayName;Similarly, you can declare arrays of other types:

byte[] anArrayOfBytes;short[] anArrayOfShorts;long[] anArrayOfLongs;float[] anArrayOfFloats;double[] anArrayOfDoubles;boolean[] anArrayOfBooleans;char[] anArrayOfChars;String[] anArrayOfStrings;

One way to create an array is with the new operator.int[ ] a; //declare a array variablea=new int[10]; //create an array of 10 integerswe can also write:a=new int[m]; //m must be initialised before

if we don’t use this statement then following error is printed:Variable a may not have been initialized.

we can also combine the above two statements into one:

int[ ] a=new int[10];

When we write this statement, a memory area for 10 integers is reserved. And a got thereference to that memory area. All elements are assigned value zero. Also a variable lengthis created which represents the total length of array i.e. total number of elements in anarray

Index

0 0 0 0 0 0 0 0 0 0

0 1 2 3 4 5 6 7 8 9

10

length

Values

Memory Address: 5000(Suppose)

5000

a a points Memory Address: 5000(Suppose)

Variable length is defined as:public final int length=10;

To access this variable we have to write:

arrayName.lengthFor example:System.out.println(a.length);will print 10Now if we write :System.out.println(a);it will print some memory address

Variable length is final i.e. constant, so we cannot write:a.length=10;this will generate an error:cannot assign a value to final variable length

Now to access any element we have to write:

a[index]where index is from 0 to length-1To access first element we have to writea[0]To access second element we have to writea[1]Similarly we can write a[9] to access last element. However, if we write a[10] it willgenerate an exception at runtime: ArrayIndexOutOfBoundsException

We can initialize array elements as:a[0]=1; a[6]=7;a[1]=2; a[7]=8;a[2]=3; a[8]=9;a[3]=4; a[9]=10;a[4]=5;a[5]=6;

We can also create an array in following manner:

int[ ] a= { 1,2,3,4,5,6,7,8,9,10};

it will create the array with given element and automatically finds its length. So thefollowing statement:System.out.println(a.length);will print 10

To print all elements of array you can use the following loop:

for(int i=0;i<a.length;i++)System.out.print(a[i]+” “);

it will print:1 2 3 4 5 6 7 8 9 10

Output:Enter the length of array: 5Enter array elements:1020304050

Array has following elements:Index 0 has element: 10Index 1 has element: 20Index 2 has element: 30Index 3 has element: 40Index 4 has element: 50

Output:Enter the length of array: 5Enter array elements:1020304050

Array has following elements:Index 0 has element: 10Index 1 has element: 20Index 2 has element: 30Index 3 has element: 40Index 4 has element: 50

The System class has an arraycopy method that you can use to efficiently copy data from one array intoanother:public static void arraycopy(Object src, int srcPos, Object dest, int destPos, int length)

The two Object arguments specify the array to copy from and the array to copy to. The three intarguments specify the starting position in the source array, the starting position in the destinationarray, and the number of array elements to copy.

class ArrayCopyDemo {public static void main(String[] args) {

char[] copyFrom = { 'd', 'e', 'c', 'a', 'f', 'f', 'e', 'i', 'n', 'a', 't', 'e', 'd' };char[] copyTo = new char[7];

System.arraycopy(copyFrom, 2, copyTo, 0, 7);System.out.println(new String(copyTo));

}}The output from this program is:

caffein

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