Single dimensional array in java

An array is a group of variable of same data type. Each element in array is assigned a unique number to identify it uniquely. This is called subscript or index. The index starts with 0.

In java an array is created in 2 steps:-

Declaring array variable:-

int arr[ ];

int [ ]arr;

These statements declare an array variable that will refer to an array that we have yet to define. No memory is allocated at this point.

Defining the array:-

arr = new int[5];

This statement creates an array of size 5 of type integer and reference to array is assigned to variable arr.

int arr[ ];                          // same as  int *arr;  in c++

arr = new int[5];             // same as arr = new int[5]; 

In java when array is created all array elements are initialised to their default value automatically.

integer default value = 0

floating default value = 0.0

boolean default value = false

character default value = '\0'                      //null

In java each array has a length variable associated with it that returns number of elements in the array.

int arr[ ] = new int[5];

System.out.print(arr.length);

This will print the array size which is 5 here.

Array index:-

We can use any arithmetic expression on an array index. If we specify an invalid index it will throw an exception at run time.
Array Index Out Of Bound Exception

A long type expression is not allowed as an array index. It is compile time error.

Example:

int a[ ]= {25, 35, 45};                 //valid

int b[ ]= new int[]{25, 35, 45};    //valid

int c[ ]= new int[3]{25, 35, 45};  //not valid as when we defined array size as 3 it is already initialised with 0.

int d[ ]= {10,20,30};                    //valid

int e[ ]= d;                                    //valid as we know int e[ ] is same as int *e in c or c++ which is a pointer                                                                        so it can point to any other memory address already existing.