Java Arrays - Java Technology | BigXStar

What is an Array?

An array is a fixed-size container that stores multiple values of the same type in contiguous memory. Each element is accessed by its index (starting from 0).

java

int[] numbers = {10, 20, 30, 40, 50};
//  Index:        0    1    2    3    4

System.out.println(numbers[0]);  // 10
System.out.println(numbers[4]);  // 50

Declaring and Initializing Arrays

java

// Method 1: Declare and initialize with values
int[] scores = {85, 92, 78, 95, 88};

// Method 2: Declare with size, then assign
int[] marks = new int[5];
marks[0] = 85;
marks[1] = 92;

// Method 3: Declare, then create
int[] grades;
grades = new int[]{90, 85, 78};

Array Properties

java

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

System.out.println(arr.length);    // 5 (number of elements)
System.out.println(arr[0]);        // 10 (first element)
System.out.println(arr[arr.length - 1]);  // 50 (last element)

Note: Array length is fixed after creation. You cannot add or remove elements. Use ArrayList for dynamic sizing.

Iterating Over Arrays

java

String[] fruits = {"Apple", "Mango", "Banana", "Grapes"};

// For loop
for (int i = 0; i < fruits.length; i++) {
    System.out.println((i + 1) + ". " + fruits[i]);
}

// For-each loop
for (String fruit : fruits) {
    System.out.println(fruit);
}

Multi-Dimensional Arrays

2D Array (Matrix)

java

int[][] matrix = {
    {1, 2, 3},
    {4, 5, 6},
    {7, 8, 9}
};

System.out.println(matrix[0][0]);  // 1
System.out.println(matrix[1][2]);  // 6

// Iterate over 2D array
for (int i = 0; i < matrix.length; i++) {
    for (int j = 0; j < matrix[i].length; j++) {
        System.out.printf("%4d", matrix[i][j]);
    }
    System.out.println();
}

Common Array Operations

Sorting

java

import java.util.Arrays;

int[] numbers = {64, 25, 12, 22, 11};
Arrays.sort(numbers);
System.out.println(Arrays.toString(numbers));
// Output: [11, 12, 22, 25, 64]

Searching

java

int[] sorted = {11, 12, 22, 25, 64};
int index = Arrays.binarySearch(sorted, 22);
System.out.println("Found at index: " + index);  // 2

Copying

java

int[] original = {1, 2, 3, 4, 5};
int[] copy = Arrays.copyOf(original, original.length);
int[] partial = Arrays.copyOfRange(original, 1, 4);  // {2, 3, 4}

Practical Example

java

public class StudentMarks {
    public static void main(String[] args) {
        String[] students = {"Arjun", "Priya", "Rahul", "Sneha", "Vikram"};
        int[] marks = {85, 92, 78, 95, 88};

        // Find highest and average
        int max = marks[0], maxIdx = 0, sum = 0;
        for (int i = 0; i < marks.length; i++) {
            sum += marks[i];
            if (marks[i] > max) {
                max = marks[i];
                maxIdx = i;
            }
        }

        double avg = (double) sum / marks.length;
        System.out.printf("Topper: %s with %d marks%n", students[maxIdx], max);
        System.out.printf("Class Average: %.1f%n", avg);
    }
}

Output:

Topper: Sneha with 95 marks
Class Average: 87.6

Summary

Arrays store fixed-size, same-type elements with zero-based indexing
Use array.length to get the size; access elements with array[index]
Java supports multi-dimensional arrays (2D, 3D, etc.)
Use java.util.Arrays for sorting, searching, copying, and printing
Arrays cannot be resized — use ArrayList for dynamic collections
ArrayIndexOutOfBoundsException occurs when accessing an invalid index