The document provides an overview of arrays in Java, detailing the structure, advantages, and disadvantages of both one-dimensional and multi-dimensional arrays. It covers how to declare, initialize, access elements, and take user input for arrays, along with examples demonstrating the use of loops for iteration. Additionally, it introduces the concept of collections as a solution to the fixed size limitation of arrays in Java.

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Array

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• An array is a collection of similar types of data.
• For example, if we want to store the names of 100
people then we can create an array of the string type
that can store 100 names.
String[] array = new String[100];
• Here, the above array cannot store more than 100
names. The number of values in a Java array is always
fixed.

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Advantages
• Code Optimization: It makes the code optimized, we
can retrieve or sort the data efficiently.
• Random access: We can get any data located at an
index position.
Disadvantages
• Size Limit: We can store only the fixed size of elements
in the array.
• It doesn't grow its size at runtime.
• To solve this problem, collection framework is used in
Java which grows automatically.

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How to declare an array in Java?
Syntax: dataType[] arrayName;
• dataType - it can be primitive data types like int, char,
double, byte, etc. or Java objects
• arrayName - it is an identifier
For example,
double[] data;
But, how many elements can array this hold?

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• To define the number of elements that an array can hold,
we have to allocate memory for the array in Java.
• For example,
// declare an array
double[] data;
// allocate memory
data = new double[10];

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• In Java, we can declare and allocate the
memory of an array in one single
statement. For example,
double[] data = new double[10];

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Initialize Arrays in Java
we can initialize arrays during declaration. For example,
//declare and initialize and array
int[] age = {12, 4, 5, 2, 5};

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In the Java array, each memory location is associated with a number.
The number is known as an array index. We can also initialize arrays in
Java, using the index number.
For example,
// declare an array
int[] age = new int[5];
// initialize array
age[0] = 12;
age[1] = 4;
age[2] = 5;
..

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Access Elements of an Array in Java
We can access the element of an array using the index
number.
// access array elements
array[index]

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class Main {
public static void main(String[] args) {
// create an array
int[] age = {12, 4, 5, 2, 5};
// access each array elements
System.out.println("Accessing Elements of Array:");
System.out.println("First Element: " + age[0]);
System.out.println("Second Element: " + age[1]);
System.out.println("Third Element: " + age[2]);
System.out.println("Fourth Element: " + age[3]);
System.out.println("Fifth Element: " + age[4]);
}
}

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Looping Through Array Elements
class Main {
public static void main(String[] args) {
// create an array
int[] age = {12, 4, 5};
// loop through the array using for loop
System.out.println("Using for Loop:");
for(int i = 0; i < age.length; i++) {
System.out.println(age[i]);
}
}
}

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Using the for-each Loop
class Main {
public static void main(String[] args) {
// create an array
int[] age = {12, 4, 5};
// loop through the array using for loop
System.out.println("Using for-each Loop:");
for(int a : age) {
System.out.println(a);
}
}
}

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Taking array through user
• Java does not provide any direct way to take array
input. But we can take array input by using the method
of the Scanner class.
• To take input of an array, we must ask the user about the
length of the array.

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One-dimensional array input
import java.util.Scanner;
public class ArrayInputExample1
{
public static void main(String[] args)
{
int n;
Scanner sc=new Scanner(System.in);
System.out.print("Enter the number of elements you want to store: ");
//reading the number of elements from the that we want to enter
n=sc.nextInt();
//creates an array in the memory of length 10
int[] array = new int[10];
System.out.println("Enter the elements of the array: ");

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for(int i=0; i<n; i++)
{
//reading array elements from the user
array[i]=sc.nextInt();
}
System.out.println("Array elements are: ");
// accessing array elements using the for loop
for (int i=0; i<n; i++)
{
System.out.println(array[i]);
}
}
}

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Java Multidimensional Arrays
• A multidimensional array is an array of arrays.
• Each element of a multidimensional array is an array
itself.
For example,
int[][] a = new int[3][4];

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How to initialize a 2d array in Java?
Here is how we can initialize a 2-dimensional array in Java.
int[][] a = {
{1, 2, 3},
{4, 5, 6, 9},
{7},
};

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Example: 2-dimensional Array
class MultidimensionalArray {
public static void main(String[] args) {
// create a 2d array
int[][] a = {
{1, 2, 3},
{4, 5, 6, 9},
{7},
};
// calculate the length of each row
System.out.println("Length of row 1: " + a[0].length);
System.out.println("Length of row 2: " + a[1].length);
System.out.println("Length of row 3: " + a[2].length);
}
}

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Printing all elements of 2d array Using Loop
class MultidimensionalArray {
public static void main(String[] args) {
int[][] a = {
{1, -2, 3},
{-4, -5, 6, 9},
{7},
};
for (int i = 0; i < a.length; ++i) {
for(int j = 0; j < a[i].length; ++j) {
System.out.println(a[i][j]);
}
}
}
}

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for...each loop to access elements
class MultidimensionalArray {
public static void main(String[] args) {
// create a 2d array
int[][] a = {
{1, -2, 3},
{-4, -5, 6, 9},
{7},
};
// first for...each loop access the individual array inside the 2d array
for (int[] innerArray: a) {
// second for...each loop access each element inside the row
for(int data: innerArray) {
System.out.println(data);
}
}
}
}

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Two-dimensional array input
• A two-dimensional array is an array that contains elements in the
form of rows and columns.
• It means we need both row and column to populate a two-
dimensional array. Matrix is the best example of a 2D array.
• We can declare a two-dimensional array by using the following
statement.
datatype arrayName[][] = new datatype[m][n];

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import java.util.Scanner;
public class ArrayInputExample2
{
public static void main(String args[])
{
int m, n, i, j;
Scanner sc=new Scanner(System.in);
System.out.print("Enter the number of rows: ");
//taking row as input
m = sc.nextInt();
System.out.print("Enter the number of columns: ");
//taking column as input
n = sc.nextInt();
// Declaring the two-dimensional matrix
int array[][] = new int[m][n];
// Read the matrix values
System.out.println("Enter the elements of the array: ");

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//loop for row
for (i = 0; i < m; i++)
//inner for loop for column
for (j = 0; j < n; j++)
array[i][j] = sc.nextInt();
//accessing array elements
System.out.println("Elements of the array are: ");
for (i = 0; i < m; i++)
{
for (j = 0; j < n; j++)
//prints the array elements
System.out.print(array[i][j] + " ");
//throws the cursor to the next line
System.out.println();
}
}

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String Array
import java.util.Scanner;
public class StringArrayInput {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
System.out.println("Enter the size of the array");
int n = sc.nextInt();
String[] arr = new String[n];
System.out.println("Enter the elements of the array");
for (int i = 0; i < n; i++) {
arr[i] = sc.next();
}
System.out.println("The elements of the array are");
for (int i = 0; i < n; i++) {
System.out.println(arr[i]);
}
}
}

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An Array Of Characters From User Input
import java.util.Scanner;
public class TakeCharArrayInputfor{
public static void main(String args[]){
//scanner class to read input from the user
Scanner sc=new Scanner(System.in);
//Declaring and creating character array
char[] arr=new char[5];
//initializing value to the array
System.out.println("******Initializing array******");
System.out.println("Enter character values");
arr=sc.next().toCharArray();
//Take character input
//displaying the array elements
System.out.println("n******displaying array of characters******");
System.out.println("Entered Characters are");
for(int i=0; i<arr.length; i++){
System.out.print(arr[i]+"t");
}
}
}

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Thanks