Hanno Embregts

Java Developer & Speaker, strong with the Force - full bio

Eleven crazy learnings from the Java 11 certification: a few freaky array declarations (1/11)

Posted on 28 Jun 2022 by Hanno Embregts java certification

In the summer of 2021, I got my Java 11 certification. I expected it to be quite a breeze, because I’d been a Java developer for 14 years and surely I should have seen it all by now, right? Turned out I was very wrong. I came across lots of things that I didn’t even know were possible with Java. In this weekly blog series I will go through 11 of these ‘crazy learnings’ that surprised me the most, even as an experienced developer. We start off with a few freaky array declarations.

Replacing array declarations by ‘var’

I really like local-varable type inference, so when the opportunity arises to replace an explicit local-variable type by var I feel really happy. When you do this for arrays, however, there is a small caveat.

You see, when I came across this line of code…

int[] elements = new int[] { 0, 1, 2, 3, 5, 8, 13, 21 };

…I just replaced int by var without thinking and thought I was done.

var[] elements = new int[] { 0, 1, 2, 3, 5, 8, 13, 21 }; // doesn't compile!

Because we’re dealing with an int array here, the square brackets are part of the data type, and so var needs to replace them also. Which will result in:

var elements = new int[] { 0, 1, 2, 3, 5, 8, 13, 21 }; // much better

It’s not a very complicated thing to remember, but it’ll surely save you some time if you do.

C-style arrays and multiple declarations on a single line

Java supports two styles of array declaration.

int[] dailyHighscores; // style 1
int allTimeHighscores[]; // style 2

The second style is called ‘C-style’ array declaration and it was added to help C programmers get used to Java. Kinda hard to imagine in a world where 18 Java versions have been released to this day, but the story seems to check out. Defining an array in C indeed means putting the brackets after the variable name, not before.

The style of array declaration used isn’t really relevant as long as we exclusively write single declarations on a single line of code only. Things get a little hairier when we start declaring multiple arrays on a single line of code.

int dailyHighscores[], allTimeHighscores; // second array is an int!

In this example, dailyHighscores is an int array, but allTimeHighscores is an int primitive! If you want both variables to be int arrays in a single declaration, you’d have to stick to the conventional style of array declaration:

int[] dailyHighscores, allTimeHighscores; // both variables are arrays now

To drive the point home, the following declaration…

int[] dailyHighscores, allTimeHighscores, highscoreMatrix[];

…would be equivalent to:

int[] dailyHighscores;
int[] allTimeHighscores;
int[][] highscoreMatrix;

So there you have it: a few freaky ways to declare arrays. Next week we’ll take a look at stream elements!

Pinball machine

Image from PxHere

Other blog posts in this series

Did you miss a blog post in this series? Here’s a list of all posts that have been published so far:

  1. A few freaky array declarations
  2. Stream elements should implement Comparable
  3. Accessing static interface methods
  4. Anonymous subclasses in enums
  5. Division by zero
  6. Method overloading priorities
  7. The crazy stuff that is allowed in switch statements
  8. Equality in cloned arrays
  9. Wrapper objects: some are more equal than others
  10. Functional interfaces actually CAN contain multiple abstract methods
  11. Passing arguments to method references