Arrays: Working with Collections

Duration: 5 min

What are Arrays?

An array is a collection of elements of the same type stored in contiguous memory locations. Arrays allow you to store multiple values in a single variable, making it easy to work with groups of related data. Each element in an array is accessed by its index, starting from 0.

Creating and Initializing Arrays

public class ArrayBasics {
    public static void main(String[] args) {
        // Method 1: Declare and specify size
        int[] numbers = new int[5];
        numbers[0] = 10;
        numbers[1] = 20;
        numbers[2] = 30;
        numbers[3] = 40;
        numbers[4] = 50;
        
        // Method 2: Initialize with values
        String[] colors = {"Red", "Green", "Blue", "Yellow"};
        
        // Method 3: Using new keyword with initialization
        double[] prices = new double[]{19.99, 29.99, 39.99};
        
        System.out.println("First number: " + numbers[0]);
        System.out.println("Array length: " + numbers.length);
        System.out.println("First color: " + colors[0]);
    }
}

First number: 10
Array length: 5
First color: Red

Accessing and Modifying Array Elements

public class ArrayOperations {
    public static void main(String[] args) {
        int[] scores = {85, 90, 78, 92, 88};
        
        // Access elements
        System.out.println("First score: " + scores[0]);
        System.out.println("Last score: " + scores[scores.length - 1]);
        
        // Modify elements
        scores[0] = 95;
        System.out.println("Updated first score: " + scores[0]);
        
        // Iterate through array
        System.out.println("All scores:");
        for (int score : scores) {
            System.out.println(score);
        }
    }
}

First score: 85
Last score: 88
Updated first score: 95
All scores:
95
90
78
92
88

Multi-dimensional Arrays

Arrays can have multiple dimensions. A 2D array is like a table with rows and columns. This is useful for representing matrices, game boards, or any grid-like data.

public class MultiDimensionalArray {
    public static void main(String[] args) {
        // 2D array - 3 rows, 3 columns
        int[][] matrix = {
            {1, 2, 3},
            {4, 5, 6},
            {7, 8, 9}
        };
        
        // Access elements
        System.out.println("Element at [0][0]: " + matrix[0][0]);
        System.out.println("Element at [1][1]: " + matrix[1][1]);
        System.out.println("Element at [2][2]: " + matrix[2][2]);
        
        // Print entire matrix
        System.out.println("\nMatrix:");
        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();
        }
    }
}

Element at [0][0]: 1
Element at [1][1]: 5
Element at [2][2]: 9

Matrix:
1 2 3 
4 5 6 
7 8 9

💡 Tip: Array indices start at 0, not 1. The last element is at index length-1. Accessing an index outside this range causes an ArrayIndexOutOfBoundsException.

Learn more: https://docs.oracle.com/javase/tutorial/java/nutsandbolts/arrays.html

💡 Tip: Pro Tip: Master Arrays thoroughly. This foundation is crucial for writing professional Java code.