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What is Array?

An array is a collection of items stored at contiguous memory locations. The idea is to store multiple items of the same type together. This makes it easier to calculate the position of each element by simply adding an offset to a base value, i.e., the memory location of the first element of the array (generally denoted by the name of the array).


// syntax of Arrays
data type[] = varible name = new data type[size];

int[] varible ={ values };

Why do we need Arrays

  • Arrays are data structures use to store a collection of data


Internal Working Arrays



Internal Representation Arrays

  • Internally in Java memory allocation totally depends on JVM whether it be continuous or not

  • Reason 1: objects are not stored in heap Memory

  • Reason 2: In JIS (Java language specification) it mentioned that heap objects are not continuous.

  • Reason 3: Dynamic Memory allocation, Hence arrays objects in Java may not be continuous (depending on Jvm)

Index of arrays


for Each loop

for ( data type  variable : arrayOrCollection) {
// Code to be executed for each element
  • for Each loop mostly used in accessing a single element value of code
public class ForEachLoopExample {
    public static void main(String[] args) {
        // Example array of integers
        int[] numbers = {1, 2, 3, 4, 5};

        // Using for-each loop to iterate over the elements in the array
        for (int num : numbers) {

Arrays to Strings

  • The java.util.Arrays.toString(int[]) method returns a string representation of the contents of the specified int array. The string representation consists of a list of the array's elements, enclosed in square brackets ("[ ]").

  • Arrays to string this store an arrays objects

import java.util.Arrays; // package 

Arrays.toString(array variable)


Arrays passing to Function

  • Arrays is an mutable

  • String is an not mutable


Multi Dimensional Arrays

  • A multidimensional array is an array of arrays.

  • Multidimensional arrays are useful when you want to store data as a tabular form, like a table with rows and columns.

int [] [] = new int [] []
int [] [] ={
//1 bracket -> rows
//2 bracket -> columns

Arrays List

The ArrayList class is a resizable which can be found in the java.util package.

The difference between a built-in array and an ArrayList in Java, is that the size of an array cannot be modified (if you want to add or remove elements to/from an array, you have to create a new one). While elements can be added and removed from an ArrayList whenever you want

import java.util.ArrayList; // import the ArrayList class

ArrayList<String> cars = new ArrayList<String>(); // Create an ArrayList object

Arrays Function

Adding Elements:

  • add(element): Adds the specified element to the end of the ArrayList.

Accessing Elements:

  • get(index): Retrieves the element at the specified index.
String element = myList.get(0); // Retrieves "Hello"

Removing Elements:

  • remove(index): Removes the element at the specified index.

  • remove(element): Removes the first occurrence of the specified element.

myList.remove(0); // Removes the first element
myList.remove("World"); // Removes "World"

Size and Checking Empty:

  • size(): Returns the number of elements in the ArrayList.

  • isEmpty(): Returns true if the ArrayList is empty.

int size = myList.size(); // Returns the number of elements
boolean empty = myList.isEmpty(); // Returns true or false

Iterating through ArrayList:

  • You can use loops or the enhanced for loop to iterate through the elements.
for (String item : myList) {

Checking for Element Existence:

  • contains(element): Returns true if the ArrayList contains the specified element.
boolean containsHello = myList.contains("Hello");

Clearing the ArrayList:

  • clear(): Removes all elements from the ArrayList.

Converting to Array:

  • toArray(): Converts the ArrayList to an array.
String[] myArray = myList.toArray(new String[0]);

Array list Internal Working


  • "Create a new ArrayList by duplicating an existing ArrayList, then add a new element. Delete the older ArrayList. Create a duplicate of the older ArrayList, copy its values, and then transfer them to the newer ArrayList."

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