Creating an array¶

When we create an array, first thing we do it declare it.

It creates a reference variable like arr that basically gives a name to the array.

The second thing is array instantiation, which allocates memory for the array in RAM. Then it updates the reference variable with an address of the first cell of the array.

This is used because we can use this address to reference each cell of the array. For example if the first cell address is X102, then we can find the second by using X102 + 1, the third X102 + 2 and so on.

The last step is to initialize the array - which basically means to assign values to the array cells.

In java we can declare 1D arrays by doing the following:

dataType[] name
int[] arr1
float[] arr2
char[] arr3

Then we can instantiate it:

arrayRefVar = new datatype[size]
arr = new int[5]

Then we can initialize it:

a[0] = 10;
a[1] = 20;
a[2] = 30;
a[3] = 40;
a[4] = 50;

We can combine all of these steps into one line by using:

int a[] = {10,20,30,40,50};

Time complexity when declaring, instantiating, initializing 1D arrays.

int[] arr -------------------------------------- O(1)
arr = new int[5] ------------------------------- O(1)
arr[0] = 10; -------------------------- O(1) -|
arr[1] = 20; -------------------------- O(1) -|
arr[2] = 30; -------------------------- O(1) -|- O(n)
arr[3] = 40; -------------------------- O(1) -|
arr[4] = 50; -------------------------- O(1) -|

int arr[] = {10,20,30,40,50} ------------------- O(1)