12. Arrays in Java

 

Arrays

• An array is a collection of similar types of data having contiguous memory allocation.
• The indexing of the array starts from 0, i.e. 1st element will be stored at the 0th index, 3rd at 2nd index and so on.
• The size of the array can not be increased at run time therefore we can store only a fixed size of elements in array.
• If the array is initialized at the time of declaration, then the dimension of the array is optional.
• An array can also be initialized by taking input of values from the keyboard with the help of loops.
• If the array elements are not given any specific values, then they contain garbage values.
• The arrays are categorized into two types as follows:
  1. One-dimensional array
  2. Multi-dimensional array

One Dimensional Array

• It is the simplest type of array.
• It is a finite set of homogeneous elements stored in contiguous memory locations.
• Declaring an array means specifying the data type and size of array.
• After arrays are declared, it can be initialized.

import java.util.Scanner;

class ArrayInJava {

    public static void main(String[] arr) {

        int[] marks1 = new int[3]; // Declaration and Memory allocation of array

        marks1[0] = 25; // Initialization of array

        marks1[1] = 16;

        marks1[2] = 21;

        int[] marks2; // Declaration of array

        marks2 = new int[3]; // Memory allocation of array

        marks2[0] = 25; // Initialization of array

        marks2[1] = 16;

        marks2[2] = 21;

        int[] marks3 = { 25, 16, 21 }; // Declaration, Memory allocation and Initialization of array

        String name[] = { "Deepak", "Chandni", "Neetu", "Sheela", "Gaurav", "Deependra", "Diksha", "Prajjwal",

                "Garvit" };

        int[] array;

        Scanner input = new Scanner(System.in);

        System.out.print("Enter the number of elements: ");

        int size = input.nextInt();

        array = new int[size];

        for (int i = 0; i < size; i++) {

            System.out.print("Enter element " + (i + 1) + ": ");

            array[i] = input.nextInt();

        }

        System.out.println("The length of your array is " + array.length);

        System.out.println("Element at index '0' in your array = " + array[0]);

input.close();

    }

}

Output :

Enter the number of elements: 5
Enter element 1: 1
Enter element 2: 2
Enter element 3: 3
Enter element 4: 4
Enter element 5: 5
The length of your array is 5
Element at index '0' in your array = 1

Accessing Array Elements

class ArrayTraversing {

    public static void main(String[] arr) {

        double[] array = { 10, 12, 14 };

        System.out.println("Printing the array using NAIVE method...");

        System.out.print(array[0] + " ");

        System.out.print(array[1] + " ");

        System.out.print(array[2] + " ");

        System.out.println("\nPrinting the array using FOR loop...");

        for (int i = 0; i < array.length; i++) {

            System.out.print(array[i] + " ");

        }

        System.out.println("\nPrinting the array using FOR-EACH loop...");

        for (double element : array) {

            System.out.print(element + " ");

        }

        System.out.println("\nPrinting the array using FOR loop in reverse order...");

        for (int i = array.length - 1; i >= 0; i--) {

            System.out.print(array[i] + " ");

        }

    }

}

Output :

Printing the array using NAIVE method...
10.0 12.0 14.0
Printing the array using FOR loop...
10.0 12.0 14.0
Printing the array using FOR-EACH loop...
10.0 12.0 14.0
Printing the array using FOR loop in reverse order...
14.0 12.0 10.0

For Each Loop in Java

• For each loop is an enhanced version of for loop and starts with the keyword for.
• Instead of declaring and initializing a loop counter variable, we declare a variable that is the same type as the base type of the array, followed by a colon, which is then followed by the array name.
• In the loop body, we can use the loop variable we created rather than using an indexed array element.
• It's commonly used to iterate over an array or a collection elements.
• The drawback of the for-each loop is that it cannot traverse the elements in reverse order.
• Moreover, we cannot skip any element while traversing.

Multi-dimensional Arrays

• It is an array of arrays' having similar data types.
• Each elements of a multi-dimensional array is an array itself.

2-D Array

class TwoDimensionalArray {

    public static void main(String[] arr) {

        int[][] flats = new int[2][3];

        flats[0][0] = 001;

        flats[0][1] = 002;

        flats[0][2] = 003;

        flats[1][0] = 101;

        flats[1][1] = 102;

        flats[1][2] = 103;

        System.out.println("Printing the 2-D array...");

        for (int i = 0; i < flats.length; i++) {

            for (int j = 0; j < flats[i].length; j++) {

                System.out.print(flats[i][j] + "\t");

            }

            System.out.print("\n");

        }

    }

}

Output :

Printing the 2-D array...
1            2          3
101       102      103

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