JAVA

Arrays

So far, we have used variables to store individual values. This works well when dealing with a small amount of data. However, many real-world applications need to store a collection of related values. For example, an e-commerce application may need to store the prices of multiple products, a weather application may need to store temperatures recorded throughout the week, or an analytics system may need to store monthly sales figures.

Creating a separate variable for every value quickly becomes difficult to manage. To solve this problem, Java provides arrays.

An array allows multiple values of the same data type to be stored under a single variable name. Each value in the array can be accessed using its position, known as an index.

In this chapter, you will learn how to create arrays, access elements, modify values, iterate through arrays, and perform common array operations.

What is an Array?

An array is a collection of multiple values stored under a single variable name.

Without an array:

double januarySales = 12000;
double februarySales = 15000;
double marchSales = 18000;
double aprilSales = 17000;

With an array:

double[] monthlySales = {12000, 15000, 18000, 17000};

Instead of creating multiple variables, all values are stored in a single array.

Creating an Array

Syntax

dataType[] arrayName = new dataType[size];

Example

int[] numbers = new int[5];

This creates an array that can store 5 integer values.

Creating and Initializing an Array

Values can also be provided when the array is created.

Example

double[] monthlySales = {12000, 15000, 18000, 17000};

This creates an array containing four sales values.

Array Indexes

Each element in an array has an index.

Indexes always start from 0.

Value : 12000  15000  18000  17000
Index :   0      1      2      3

The first element is stored at index 0, the second at index 1, and so on.

Accessing Array Elements

Array elements are accessed using their index.

Example

double[] monthlySales = {12000, 15000, 18000, 17000};

System.out.println(monthlySales[0]);

Output

12000.0

Java retrieves the value stored at index 0.

Accessing Different Elements

Example

double[] monthlySales = {12000, 15000, 18000, 17000};

System.out.println(monthlySales[2]);

Output

18000.0

Since 18000 is stored at index 2, that value is displayed.

Updating Array Elements

Values inside an array can be modified.

Example

double[] monthlySales = {12000, 15000, 18000, 17000};

monthlySales[1] = 20000;

System.out.println(monthlySales[1]);

Output

20000.0

The value at index 1 is replaced with 20000.

Finding the Length of an Array

The length property returns the number of elements in an array.

Example

double[] monthlySales = {12000, 15000, 18000, 17000};

System.out.println(monthlySales.length);

Output

4

Traversing an Array Using a for Loop

Arrays are commonly processed using loops.

Example

double[] monthlySales = {12000, 15000, 18000, 17000};

for(int i = 0; i < monthlySales.length; i++) {
    System.out.println(monthlySales[i]);
}

Output

12000.0
15000.0
18000.0
17000.0

Explanation

• The loop starts from index 0.
• It continues until the last index.
• During each iteration, one element is displayed.

Enhanced for Loop (for-each)

Java provides a simpler way to iterate through arrays.

Syntax

for(dataType variable : arrayName) {

}

Example

double[] monthlySales = {12000, 15000, 18000, 17000};

for(double sale : monthlySales) {
    System.out.println(sale);
}

Output

12000.0
15000.0
18000.0
17000.0

The enhanced for loop automatically visits each element in the array.

Complete Program

Example

public class Main {

    public static void main(String[] args) {

        double[] monthlySales = {12000, 15000, 18000, 17000};

        double totalSales = 0;

        for(int i = 0; i < monthlySales.length; i++) {
            totalSales += monthlySales[i];
        }

        System.out.println("Total Sales = " + totalSales);
    }
}

Output

Total Sales = 62000.0

Explanation

• An array stores monthly sales values.
• A loop visits each element.
• Each value is added to totalSales.
• The final sales amount is displayed.

Common Mistakes

Accessing an Invalid Index

Wrong

double[] sales = {12000, 15000, 18000};

System.out.println(sales[3]);

Problem

Valid indexes are:

0
1
2

Index 3 does not exist and causes an error.

Correct

System.out.println(sales[2]);

Starting From Index 1

Wrong

System.out.println(sales[1]);

Expecting the first element.

Problem

Arrays start at index 0.

Correct

System.out.println(sales[0]);

Key Takeaways

• An array stores multiple values of the same data type.
• Array indexes start from 0.
• Elements are accessed using their index.
• Array values can be updated.
• The length property returns the number of elements.
• Loops are commonly used to process arrays.
• The enhanced for loop provides a simpler way to traverse arrays.
• Arrays help organize and manage collections of related data efficiently.