Java Arrays

Java arrays store a fixed number of values of the same type in a single variable. Each value has an index starting at 0, and the size is set when the array is created and cannot change.

Creating and Accessing Arrays

public class Main {
    public static void main(String[] args) {
        int[] temps = {31, 28, 35, 30};
        String[] names = new String[3]; // three empty slots (null)
        names[0] = "Ali";
        names[1] = "Sara";

        System.out.println(temps[2]);
        temps[2] = 33;
        System.out.println(temps[2]);
        System.out.println("Length: " + temps.length);
        System.out.println(names[2]);
    }
}

35
33
Length: 4
null

new String[3] creates an array of three elements filled with default values: null for objects, 0 for numbers and false for booleans. Accessing index 4 of a four-element array throws ArrayIndexOutOfBoundsException.

Looping Through an Array

public class Main {
    public static void main(String[] args) {
        double[] prices = {4.5, 12.0, 7.25};
        double sum = 0;
        for (int i = 0; i < prices.length; i++) {
            System.out.println("Item " + i + ": " + prices[i]);
            sum += prices[i];
        }
        System.out.println("Total: " + sum);
    }
}

Item 0: 4.5
Item 1: 12.0
Item 2: 7.25
Total: 23.75

The Arrays Utility Class

java.util.Arrays has ready-made methods for sorting, printing, searching, filling and copying arrays.

import java.util.Arrays;

public class Main {
    public static void main(String[] args) {
        int[] nums = {42, 7, 19, 3, 25};
        System.out.println(Arrays.toString(nums));
        Arrays.sort(nums);
        System.out.println(Arrays.toString(nums));
        System.out.println(Arrays.binarySearch(nums, 19));
        int[] bigger = Arrays.copyOf(nums, 7);
        System.out.println(Arrays.toString(bigger));
        System.out.println(Arrays.stream(nums).max().getAsInt());
    }
}

[42, 7, 19, 3, 25]
[3, 7, 19, 25, 42]
2
[3, 7, 19, 25, 42, 0, 0]
42

Printing an array directly with println shows something like [I@1b6d3586, a type code and hash, not the contents. Use Arrays.toString instead.

Two-Dimensional Arrays

A 2D array is an array of arrays, perfect for tables and grids. Use two indexes: [row][column].

public class Main {
    public static void main(String[] args) {
        int[][] grid = {
            {1, 2, 3},
            {4, 5, 6}
        };
        System.out.println(grid[1][2]);
        for (int[] row : grid) {
            for (int value : row) {
                System.out.print(value + " ");
            }
            System.out.println();
        }
    }
}

6
1 2 3
4 5 6 

Frequently asked questions

How do I find the length of an array in Java?

Use the length field without parentheses: myArray.length. Strings use a length() method, which is a common point of confusion.

Can a Java array change size?

No. Arrays have a fixed size. Create a bigger copy with Arrays.copyOf, or use an ArrayList, which grows automatically.

How do I print an array in Java?

Use Arrays.toString(array) for one-dimensional arrays and Arrays.deepToString(array) for multi-dimensional arrays.