Codectionary / Developer documentation / Java

Arrays

An array in Java is a fixed-size, ordered collection of elements of the same type, stored in contiguous memory for efficient access. Once created, an array's length cannot change - if you need a resizable collection, use an ArrayList instead. Arrays can be one-dimensional or multi-dimensional (arrays of arrays), and are zero-indexed like most Java collections.

Syntax

type[] arrayName = new type[size];

Examples

Creating and Accessing Arrays

Declaring arrays with initial values and reading elements by index.

int[] numbers = {10, 20, 30, 40, 50};
String[] names = new String[3];
names[0] = "John";
names[1] = "Zain";
names[2] = "Jamal";

System.out.println(numbers[0]);   // 10
System.out.println(numbers.length); // 5
System.out.println(names[1]);      // Zain

Iterating Over an Array

Looping through array elements with a standard for loop or an enhanced for-each loop.

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

for (int i = 0; i < scores.length; i++) {
    System.out.println("Index " + i + ": " + scores[i]);
}

// Enhanced for-each loop - simpler when you don't need the index
for (int score : scores) {
    System.out.println(score);
}

Multi-Dimensional Arrays

Creating and accessing a 2D array, 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 1, column 2)

for (int[] row : grid) {
    for (int value : row) {
        System.out.print(value + " ");
    }
    System.out.println();
}

Common Array Operations with java.util.Arrays

Using the built-in Arrays utility class for sorting, filling, and printing.

import java.util.Arrays;

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

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

int[] filled = new int[5];
Arrays.fill(filled, 7);
System.out.println(Arrays.toString(filled));   // [7, 7, 7, 7, 7]

Best practices

  • Use an ArrayList instead of a plain array whenever the collection needs to grow or shrink dynamically
  • Use the enhanced for-each loop when you just need the values, and a standard indexed loop when you need the index too
  • Use Arrays.toString() (or Arrays.deepToString() for 2D arrays) to print array contents readably - printing an array directly shows its memory reference, not its contents
  • Always check array.length before accessing an index in a loop to avoid an ArrayIndexOutOfBoundsException

Runtime & versions

Java Virtual Machine. Feature availability depends on the language and runtime version used by your project; consult the official reference below.

Java Language Specification

Specifications & further reading