Arrays

What is an Array?

An array is a fixed-size container that stores multiple values of the same type under one variable name. Instead of creating score1, score2, score3, you can store them all in a single array.

Declaring and Creating Arrays

// Declare and initialize with values directly
int[] scores = {85, 90, 78, 92, 88};

// Declare, then create with a fixed size
int[] numbers = new int[5]; // creates an array of 5 zeros
numbers[0] = 10;
numbers[1] = 20;

    Note: Array indexing starts at 0, not 1. So in an array of 5 elements, valid indexes are 0 through 4.

Accessing and Updating Elements

int[] scores = {85, 90, 78, 92, 88};

System.out.println(scores[0]); // 85, the first element
System.out.println(scores[4]); // 88, the last element

scores[2] = 100; // update the third element
System.out.println(scores[2]); // 100

Finding the Length

Every array has a built-in length property (note: no parentheses, unlike a method call).

int[] scores = {85, 90, 78, 92, 88};
System.out.println(scores.length); // 5

Looping Through an Array

int[] scores = {85, 90, 78, 92, 88};

// Using a standard for loop
for (int i = 0; i < scores.length; i++) {
    System.out.println("Score " + i + ": " + scores[i]);
}

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

Multidimensional Arrays

Java supports arrays of arrays, most commonly used to represent grids or matrices.

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

System.out.println(grid[1][2]); // 6 (row index 1, column index 2)

for (int row = 0; row < grid.length; row++) {
    for (int col = 0; col < grid[row].length; col++) {
        System.out.print(grid[row][col] + " ");
    }
    System.out.println();
}

Arrays of Other Types

String[] names = {"Alice", "Bob", "Charlie"};
double[] prices = {19.99, 5.49, 100.0};
boolean[] flags = {true, false, true};

Common Array Utility Methods

The java.util.Arrays class provides handy helper methods:

import java.util.Arrays;

int[] numbers = {5, 2, 8, 1, 9};

Arrays.sort(numbers);                  // sorts in place: [1, 2, 5, 8, 9]
System.out.println(Arrays.toString(numbers)); // prints [1, 2, 5, 8, 9]

    Important: Arrays in Java have a fixed size once created — you cannot add or remove elements. If you need a resizable collection, use an ArrayList from the Java Collections Framework instead.

    Coming up next: Methods — how to organize your code into reusable, named blocks.