Arrays are fundamental data structures in Java that store multiple values of the same type in a single variable.

Array Characteristics

  • Fixed size: Once created, the size cannot be changed
  • Indexed: Elements are accessed by their index (starting at 0)
  • Homogeneous: All elements must be of the same type
  • Contiguous memory: Elements are stored in consecutive memory locations

Declaring Arrays 

// Different ways to declare arrays
int[] numbers1;          // Preferred syntax
int numbers2[];          // Alternative syntax (less common)

Creating Arrays 

// Creating arrays with size
int[] numbers = new int[5];  // Array of 5 integers (initialized to 0)

// Creating and initializing in one line
String[] names = {"Alice", "Bob", "Charlie"};

Accessing Array Elements 

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

// Accessing elements
System.out.println(numbers[0]);  // Output: 10
System.out.println(numbers[2]);  // Output: 30

// Modifying elements
numbers[1] = 25;

Array Length 

int[] numbers = {10, 20, 30};
System.out.println(numbers.length);  // Output: 3

Iterating Through Arrays 

// Using for loop
for (int i = 0; i < numbers.length; i++) {
    System.out.println(numbers[i]);
}

// Using enhanced for loop (for-each)
for (int num : numbers) {
    System.out.println(num);
}

Multidimensional Arrays 

// 2D array (matrix)
int[][] matrix = new int[3][3];  // 3x3 matrix

// Initializing 2D array
int[][] grid = {
    {1, 2, 3},
    {4, 5, 6},
    {7, 8, 9}
};

// Accessing elements
System.out.println(grid[1][2]);  // Output: 6

Common Array Operations 

// Sorting
Arrays.sort(numbers);

// Searching (array must be sorted)
int index = Arrays.binarySearch(numbers, 20);

// Copying
int[] copy = Arrays.copyOf(numbers, numbers.length);

// Filling
Arrays.fill(numbers, 0);  // Sets all elements to 0

// Comparing
boolean equal = Arrays.equals(array1, array2);

Important Notes

  1. Array indices range from 0 to length-1
  2. Accessing an invalid index throws ArrayIndexOutOfBoundsException
  3. Arrays are objects in Java (even primitive arrays)
  4. The length property is final and cannot be changed

Array Limitations

  • Fixed size (use ArrayList if you need dynamic sizing)
  • No built-in methods for common operations (use Arrays utility class)
  • Memory waste if array is larger than needed