What is an Array in Java?

An array in Java is a collection of similar data type values stored in a single variable.

For example, if we want to store marks of five students, we can write:

int marks[] = {80, 85, 90, 75, 88};

Here, marks is an array that stores five integer values.

Without an array, we would need to create separate variables:

int mark1 = 80;
int mark2 = 85;
int mark3 = 90;
int mark4 = 75;
int mark5 = 88;

This approach is not good for large data. Arrays make the program shorter, cleaner, and easier to manage.

How Arrays Work in Java

Arrays work on the basis of index numbers. Each value inside an array is called an element, and every element has a specific index position.

Java array indexing starts from 0.

Example:

int marks[] = {80, 85, 90, 75, 88};

To access an array element, we use the array name with the index number.

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

Output:

80

Here, marks[0] gives the first value of the array.

Array Declaration in Java

An array can be declared in two ways:

dataType arrayName[];

or

dataType[] arrayName;

Example:

int numbers[];

or

int[] numbers;

Both are valid, but int[] numbers; is commonly used because it clearly shows that numbers is an integer array.

Array Creation in Java

An array is created using the new keyword.

int numbers[] = new int[5];

This creates an integer array that can store 5 values.

We can assign values like this:

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

Array Initialization in Java

Array initialization means assigning values to an array.

We can initialize an array directly:

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

This is the easiest way when we already know the values.

Accessing Array Elements

Array elements are accessed using index numbers.

public class ArrayExample {
    public static void main(String[] args) {
        int numbers[] = {10, 20, 30, 40, 50};

        System.out.println(numbers[0]);
        System.out.println(numbers[1]);
        System.out.println(numbers[2]);
    }
}

Output:

10
20
30

Traversing an Array

Traversing means accessing all elements of an array one by one. We usually use loops to traverse arrays.

public class ArrayTraversal {
    public static void main(String[] args) {
        int marks[] = {80, 85, 90, 75, 88};

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

Output:

80
85
90
75
88

Here, marks.length gives the total number of elements in the array.

Enhanced For Loop with Array

Java also provides an enhanced for loop to read array elements easily.

public class EnhancedForLoopExample {
    public static void main(String[] args) {
        int numbers[] = {10, 20, 30, 40, 50};

        for(int num : numbers) {
            System.out.println(num);
        }
    }
}

Output:

10
20
30
40
50

The enhanced for loop is useful when we only want to read values from an array.

Types of Arrays in Java

There are mainly two types of arrays in Java:

1. One-Dimensional Array
2. Two-Dimensional Array

One-Dimensional Array

A one-dimensional array stores data in a single row or list format.

Example:

int marks[] = {80, 85, 90, 75, 88};

This type of array is useful for storing simple list-based data like marks, roll numbers, prices, or ages.

Example program:

public class OneDArray {
    public static void main(String[] args) {
        int marks[] = {80, 85, 90, 75, 88};

        for(int i = 0; i < marks.length; i++) {
            System.out.println("Marks: " + marks[i]);
        }
    }
}

Two-Dimensional Array

A two-dimensional array stores data in rows and columns. It is also called a matrix.

Example:

int matrix[][] = {
    {1, 2, 3},
    {4, 5, 6}
};

Here, the array has 2 rows and 3 columns.

To access a value from a two-dimensional array, we use two index numbers:

System.out.println(matrix[0][1]);

Output:

2

Here, 0 is the row index and 1 is the column index.

Example program:

public class TwoDArray {
    public static void main(String[] args) {
        int matrix[][] = {
            {1, 2, 3},
            {4, 5, 6}
        };

        for(int i = 0; i < matrix.length; i++) {
            for(int j = 0; j < matrix[i].length; j++) {
                System.out.print(matrix[i][j] + " ");
            }
            System.out.println();
        }
    }
}

Output:

1 2 3
4 5 6

Important Points About Arrays

• Arrays store multiple values in a single variable.
• Arrays can store only the same type of data.
• Array indexing starts from 0.
• Array size is fixed after creation.
• Array elements are accessed using index numbers.
• The length property is used to find the size of an array.
• Arrays work very well with loops.
• Arrays can be one-dimensional or multi-dimensional.

Advantages of Arrays

Arrays are useful because they help store and manage multiple values easily. They reduce the need to create many separate variables. Arrays also make it easier to process data using loops.

For example, we can calculate total marks, find the largest number, search for an element, or print all values using arrays.

Limitations of Arrays

Arrays also have some limitations. The size of an array is fixed, so we cannot easily increase or decrease its size after creation. Arrays can store only one type of data. If we need a flexible structure where data can be added or removed easily, then Java Collections such as ArrayList are better.

Real-Life Example of Array

Suppose a teacher wants to store marks of 5 students. Instead of creating 5 different variables, the teacher can use one array.

int studentMarks[] = {78, 85, 92, 67, 89};

Now the teacher can easily print all marks, calculate total marks, find average marks, or find the highest marks using loops.

Practice Programs for Students

Students should practice the following programs after learning arrays:

1. Print all elements of an array
2. Find the sum of array elements
3. Find the largest number in an array
4. Find the smallest number in an array
5. Search an element in an array
6. Reverse an array
7. Count even and odd numbers in an array
8. Print a two-dimensional array
9. Add two matrices
10. Find the average marks of students

Conclusion

Arrays in Java are used to store multiple values of the same data type in a single variable. They help make programs cleaner, shorter, and easier to manage. Arrays are very useful when working with list-based or table-based data.

In this lesson, students learned array declaration, array creation, initialization, indexing, accessing elements, traversing arrays using loops, one-dimensional arrays, two-dimensional arrays, advantages, limitations, and practical uses of arrays.

After completing arrays, the next important topic is Strings in Java, where students will learn how to store and process text data in Java.