Module 2: Arrays

Array Declaration and Initialization

Arrays store multiple values of the same data type with a fixed size determined at creation.

// Method 1: Declaration and initialization in two steps
int[] numbers;           // Declaration
numbers = new int[5];    // Initialization with size 5

// Method 2: Declaration and initialization in one step
int[] scores = new int[10];  

// Method 3: Declaration with initialization and values
int[] primes = {2, 3, 5, 7, 11};
                

Default Values

When you create an array, elements are automatically initialized with default values:

// Primitive type arrays are initialized with zeros/false
int[] numbers = new int[3];       // {0, 0, 0}
boolean[] flags = new boolean[2]; // {false, false}

// Object arrays are initialized with null
String[] names = new String[3];   // {null, null, null}
                

Accessing and Modifying Array Elements

Array elements are accessed using zero-based indexing.

int[] scores = {85, 92, 78, 95, 88};

// Accessing elements
int firstScore = scores[0];   // 85
int thirdScore = scores[2];   // 78

// Modifying elements
scores[1] = 94;               // Array becomes {85, 94, 78, 95, 88}
                

Array Length

The length of an array is fixed at creation time and can be accessed using the length property.

int[] numbers = {10, 20, 30, 40, 50};
int arrayLength = numbers.length;  // 5

// Common pattern: Looping through array elements
for (int i = 0; i < numbers.length; i++) {
    System.out.println("Element at index " + i + ": " + numbers[i]);
}
                

For-Each Loop with Arrays

The enhanced for loop (for-each) provides a simpler way to iterate through arrays.

int[] scores = {85, 92, 78, 95, 88};

// Using for-each loop
for (int score : scores) {
    System.out.println("Score: " + score);
}
                

Multi-dimensional Arrays

Java supports multi-dimensional arrays, which are essentially arrays of arrays.

// 2D array declaration and initialization
int[][] matrix = {
    {1, 2, 3},
    {4, 5, 6},
    {7, 8, 9}
};

// Accessing elements in a 2D array
int element = matrix[1][2];  // Row 1, Column 2: value is 6

// Looping through a 2D array
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();
}
                

• Arrays Practice Repository
• Java Arrays Documentation
• Array Data Structure Guide

• Create and manipulate single-dimensional arrays
• Implement array sorting algorithms
• Work with multi-dimensional arrays
• Solve array-based problems