Java arrays, Wat!?

There is a few things you can do with arrays which are surprising.
 
 
 
 
 
 
 
 
 
 

Is it an array or not?

Serializable array = new Serializable[9];

Is array an array or a scalar? Well its a scalar which points to an array. Just like 

Object o = new Object[9];

You can assign an array to an object because it is also an object.  However, arrays are also Serializable so you can assign them to Serializable.

Where did my [] go?

The [] can appear in surprising places.  This compiles for backward comparability reasons.

public static int method(int[]... args)[] {
    return args[0];
}

And the types here are; args is an int[][] and the return type is int[].  Did you notice the [] after the method declaration!  This is not part of the JLS and the OpenJDK allows this due to backward compatibility reasons.

What is the difference between int[] array and int array[] ?

There is a difference in what comes after it.

int[] array, x[];

and

int array[], y[];

In these cases; x is an int[][] but y is only an int[].

What happens if an array initialization is too large?

Say I initialize an array like this

public static final int[] VALUES = {
    1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,
            /* many, many lines deleted */
    1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,
};

The errors message is;

Error:(6, 31) java: code too large

This seems a little strange.  It doesn’t complain the array is too large.  In fact if I have more static fields or use larger constants, it will fail for a smaller array.
 
This happens because arrays are initialised in byte code.  There byte code creates the array and initialises each value, one at a time.  This results in a lot of code for large arrays which would be such a problem if there wasn’t a limit in the size of a method. i.e. 65535 bytes.  The compiler generates one and only one method for a constructor or static initialization so this limits how many enums you can have and how large your initialised arrays can be.

Reference: Java arrays, Wat!? from our JCG partner Peter Lawrey at the Vanilla Java blog.

Do you want to know how to develop your skillset to become a Java Rockstar?

Subscribe to our newsletter to start Rocking right now!

To get you started we give you two of our best selling eBooks for FREE!

JPA Mini Book

Learn how to leverage the power of JPA in order to create robust and flexible Java applications. With this Mini Book, you will get introduced to JPA and smoothly transition to more advanced concepts.

JVM Troubleshooting Guide

The Java virtual machine is really the foundation of any Java EE platform. Learn how to master it with this advanced guide!

Given email address is already subscribed, thank you!
Oops. Something went wrong. Please try again later.
Please provide a valid email address.
Thank you, your sign-up request was successful! Please check your e-mail inbox.
Please complete the CAPTCHA.
Please fill in the required fields.

Leave a Reply


+ nine = 14



Java Code Geeks and all content copyright © 2010-2014, Exelixis Media Ltd | Terms of Use | Privacy Policy | Contact
All trademarks and registered trademarks appearing on Java Code Geeks are the property of their respective owners.
Java is a trademark or registered trademark of Oracle Corporation in the United States and other countries.
Java Code Geeks is not connected to Oracle Corporation and is not sponsored by Oracle Corporation.
Do you want to know how to develop your skillset and become a ...
Java Rockstar?

Subscribe to our newsletter to start Rocking right now!

To get you started we give you two of our best selling eBooks for FREE!

Get ready to Rock!
You can download the complementary eBooks using the links below:
Close