Java · Lesson 8 of 15

Arrays

Fixed-size arrays, loops over them, 2D arrays and the Arrays utility class.

Beginner
12 min read
3 objectives

Before this lessonLesson 7: Strings and StringBuilder

What you will learn

Create and index arrays
Loop with for and for-each
Sort and print with Arrays

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An array holds a fixed number of values of one type, stored side by side and accessed by index starting at 0. The length is set when you create it and cannot change.

Creating and reading

public class Main {
    public static void main(String[] args) {
        int[] scores = new int[3];      // {0, 0, 0}
        scores[0] = 90;
        int[] primes = {2, 3, 5, 7};
        System.out.println(scores[0] + " " + primes.length);
        System.out.println(primes[primes.length - 1]);
    }
}

Output

90 4
7

Reading past the end throws ArrayIndexOutOfBoundsException; valid indexes are 0 to length - 1.

Looping

public class Main {
    public static void main(String[] args) {
        int[] nums = {4, 8, 15};
        int sum = 0;
        for (int n : nums) {
            sum += n;
        }
        System.out.println(sum);
        for (int i = 0; i < nums.length; i++) {
            System.out.println(i + ": " + nums[i]);
        }
    }
}

Output

The Arrays helper class

import java.util.Arrays;

public class Main {
    public static void main(String[] args) {
        int[] a = {5, 2, 9, 1};
        Arrays.sort(a);
        System.out.println(Arrays.toString(a));
        System.out.println(Arrays.binarySearch(a, 5));
        int[] copy = Arrays.copyOf(a, 6);
        System.out.println(Arrays.toString(copy));
        System.out.println(Arrays.equals(a, copy));
    }
}

Output

[1, 2, 5, 9]
2
[1, 2, 5, 9, 0, 0]
false

Two-dimensional arrays

import java.util.Arrays;

public class Main {
    public static void main(String[] args) {
        int[][] grid = {{1, 2, 3}, {4, 5, 6}};
        System.out.println(grid[1][2]);
        System.out.println(Arrays.deepToString(grid));
    }
}

Output

6
[[1, 2, 3], [4, 5, 6]]

Up next · Lesson 9Methods and OverloadingParameters, return values, overloading, varargs and pass-by-value.