Search icon CANCEL
Subscription
0
Cart icon
Your Cart (0 item)
Close icon
You have no products in your basket yet
Save more on your purchases! discount-offer-chevron-icon
Savings automatically calculated. No voucher code required.
Arrow left icon
Explore Products
Best Sellers
New Releases
Books
Videos
Audiobooks
Learning Hub
Newsletter Hub
Free Learning
Arrow right icon
timer SALE ENDS IN
0 Days
:
00 Hours
:
00 Minutes
:
00 Seconds
Clojure for Java Developers
Clojure for Java Developers

Clojure for Java Developers: Transition smoothly from Java to the most widely used functional JVM-based language – Clojure

Free Trial
Paperback Feb 2016 156 pages 1st Edition
eBook
Can$13.99 Can$39.99
Paperback
Can$49.99
Subscription
Free Trial
Free Trial
Paperback Feb 2016 156 pages 1st Edition
eBook
Can$13.99 Can$39.99
Paperback
Can$49.99
Subscription
Free Trial
eBook
Can$13.99 Can$39.99
Paperback
Can$49.99
Subscription
Free Trial

What do you get with a Packt Subscription?

Free for first 7 days. $19.99 p/m after that. Cancel any time!
Product feature icon Unlimited ad-free access to the largest independent learning library in tech. Access this title and thousands more!
Product feature icon 50+ new titles added per month, including many first-to-market concepts and exclusive early access to books as they are being written.
Product feature icon Innovative learning tools, including AI book assistants, code context explainers, and text-to-speech.
Product feature icon Thousands of reference materials covering every tech concept you need to stay up to date.
Subscribe now
View plans & pricing
Table of content icon View table of contents Preview book icon Preview Book

Clojure for Java Developers

Chapter 2. Namespaces, Packages, and Tests

We now have a working installation of Clojure and IntelliJ.

As a Java developer, you are used to working with classes as the minimal unit of organization. Clojure has a very different sense and gives you different tools to organize your code.

For starters, you should keep in mind that code and data are separate; you don't have a minimal unit with attributes and functions that work over those attributes. Your functions can work on any data structure that you wish, as long as you follow the rules of how the function works.

In this chapter, we will start writing some simple functions to illustrate how separation of functions and data works and we will have a look at the tools Clojure gives us to make the separation.

In this chapter, we will cover the following topic:

  • How namespaces work compared to the classpath and Java packages
  • Unit tests
  • More Clojure examples and syntax

Namespaces in Clojure

Clojure namespaces might be familiar to you, as a Java developer, and for a very good reason, they have a very deep relationship with Java's packages and the classpath.

First of all, let's review what we already know from Java.

Packages in Clojure

The Java code is organized in packages, a package in Java is a namespace that allows you to group a set of similar classes and interfaces.

You can think of a package as something very similar to a folder in your computer.

The following are some common packages that you use a lot when programming in Java:

  • java.lang: Everything that's native to Java, including basic types (integer, long, byte, boolean, character, string, number, short, float, void, and class), the basic threading primitives (runnable, thread), the basic primitives for exceptions (throwable, error, exception), the basic exceptions and errors (NoSuchMethodError, OutOfMemoryError, StackOverflowError, and so on) and runtime access classes like runtime...

The classpath and the classloader

Java was designed to be modular and for that it needs some way to load your code easily. The answer to this was the classloader, the classloader allows you to read resources from every entry of the classpath; you can look at resources in the classpath as a hierarchical structure similar to the file system.

The classloader is just a list of entries; each entry can be a directory in the filesystem or a JAR file. At this point, you should also know that JAR files are just zip files.

The classloader will treat each entry as a directory (JAR files are just zipped directories) and it will look for files in each directory.

There are a lot of concepts here to remember, let's try to summarize them:

  • JAR files are ZIP files; they might contain several classes, properties, files, and so on.
  • The classpath is a list of entries; each entry is a JAR file or a system directory.
  • The classloader looks for resources in each entry of the classpath, so you can think of classpath...

Testing in Clojure

Clojure already comes with a unit testing support built-in, as a matter of fact Leiningen has already created a test for us; let's take a look at it right now.

Open the test/ns_playground/core_test.clj file, you should be able to see this code:

(ns ns-playground.core-test
  (:require [clojure.test :refer :all]
            [ns-playground.core :refer :all]))
(deftest a-test
  (testing "FIXME, I fail."
(is (= 0 1))))

Again, as you can see, we are using :require to include functions from the clojure.test and the ns-playground.core packages.

Note

Remember, the :refer :all works similar to how char import static clojure.test.* will work in Java.

Testing from the command line

Let's first learn how to run these tests. From the command line, you can run:

lein test

You should get the following output:

lein test ns-playground.core-test

lein test :only ns-playground.core-test/a-test

FAIL in (a-test) (core_test.clj:7)
FIXME, I fail.
expected: (= 0 1)
  actual: (not (...

Summary

In this chapter, we got to know some utilities that we can use for better management of our code and we have some more examples of everyday Clojure code. In particular:

  • Working of namespace in Clojure and their relation to Java packages
  • Writing out-of-the-box unit tests and executing them with Leiningen and Cursive Clojure
  • Delving into the Clojure Interactive development workflow and a bit of the Clojure mindset
  • Writing very simple functions and testing them

In the next chapter, we will learn about Java interop, so we can start using the familiar classes and libraries we already know in our Clojure code.

We will also learn how to use Clojure from Java, so you can start using it in your everyday Java projects.

Left arrow icon Right arrow icon

Key benefits

  • *Write apps for the multithreaded world with Clojure’s flavor of functional programming
  • *Discover Clojure’s features and advantages and use them in your existing projects
  • *The book is designed so that you’ll be able put to use your existing skills and software knowledge to become a more effective Clojure developer

Description

We have reached a point where machines are not getting much faster, software projects need to be delivered quickly, and high quality in software is more demanding as ever. We need to explore new ways of writing software that helps achieve those goals. Clojure offers a new possibility of writing high quality, multi-core software faster than ever, without having to leave your current platform. Clojure for Java developers aims at unleashing the true potential of the Clojure language to use it in your projects. The book begins with the installation and setup of the Clojure environment before moving on to explore the language in-depth. Get acquainted with its various features such as functional programming, concurrency, etc. with the help of example projects. Additionally, you will also, learn how the tooling works, and how it interacts with the Java environment. By the end of this book, you will have a firm grip on Clojure and its features, and use them effectively to write more robust programs.

Who is this book for?

This book is intended for Java developers, who are looking for a way to expand their skills and understand new paradigms of programming. Whether you know a little bit about functional languages, or you are just getting started, this book will get you up and running with how to use your existing skills in Clojure and functional programming.

What you will learn

  • *Understand the tools for the Clojure world and how they relate to Java tools and standards (like Maven)
  • *Learn about immutable data structures, and what makes them feasible for everyday programming
  • *Write simple multi-core programs using Clojure's core concepts, like atoms, agents and refs
  • *Understand that in Clojure, code is data, and how to take advantage of that fact by generating and manipulating code with macros
  • *Learn how Clojure interacts with Java, how the class loaders work and how to use Clojure from Java or the other way around
  • *Discover a new, more flexible meaning of polymorphism and understand that OOP is not the only way to get it

Product Details

Country selected
Publication date, Length, Edition, Language, ISBN-13
Publication date : Feb 23, 2016
Length: 156 pages
Edition : 1st
Language : English
ISBN-13 : 9781785281501
Category :
Languages :

What do you get with a Packt Subscription?

Free for first 7 days. $19.99 p/m after that. Cancel any time!
Product feature icon Unlimited ad-free access to the largest independent learning library in tech. Access this title and thousands more!
Product feature icon 50+ new titles added per month, including many first-to-market concepts and exclusive early access to books as they are being written.
Product feature icon Innovative learning tools, including AI book assistants, code context explainers, and text-to-speech.
Product feature icon Thousands of reference materials covering every tech concept you need to stay up to date.
Subscribe now
View plans & pricing

Product Details

Publication date : Feb 23, 2016
Length: 156 pages
Edition : 1st
Language : English
ISBN-13 : 9781785281501
Category :
Languages :

Packt Subscriptions

See our plans and pricing
Modal Close icon
$19.99 billed monthly
Feature tick icon Unlimited access to Packt's library of 7,000+ practical books and videos
Feature tick icon Constantly refreshed with 50+ new titles a month
Feature tick icon Exclusive Early access to books as they're written
Feature tick icon Solve problems while you work with advanced search and reference features
Feature tick icon Offline reading on the mobile app
Feature tick icon Simple pricing, no contract
$199.99 billed annually
Feature tick icon Unlimited access to Packt's library of 7,000+ practical books and videos
Feature tick icon Constantly refreshed with 50+ new titles a month
Feature tick icon Exclusive Early access to books as they're written
Feature tick icon Solve problems while you work with advanced search and reference features
Feature tick icon Offline reading on the mobile app
Feature tick icon Choose a DRM-free eBook or Video every month to keep
Feature tick icon PLUS own as many other DRM-free eBooks or Videos as you like for just Can$6 each
Feature tick icon Exclusive print discounts
$279.99 billed in 18 months
Feature tick icon Unlimited access to Packt's library of 7,000+ practical books and videos
Feature tick icon Constantly refreshed with 50+ new titles a month
Feature tick icon Exclusive Early access to books as they're written
Feature tick icon Solve problems while you work with advanced search and reference features
Feature tick icon Offline reading on the mobile app
Feature tick icon Choose a DRM-free eBook or Video every month to keep
Feature tick icon PLUS own as many other DRM-free eBooks or Videos as you like for just Can$6 each
Feature tick icon Exclusive print discounts

Frequently bought together


Stars icon
Total Can$ 175.97
Mastering Clojure
Can$69.99
Learning ClojureScript
Can$55.99
Clojure for Java Developers
Can$49.99
Total Can$ 175.97 Stars icon

Table of Contents

8 Chapters
1. Getting Started with Clojure Chevron down icon Chevron up icon
2. Namespaces, Packages, and Tests Chevron down icon Chevron up icon
3. Interacting with Java Chevron down icon Chevron up icon
4. Collections and Functional Programming Chevron down icon Chevron up icon
5. Multimethods and Protocols Chevron down icon Chevron up icon
6. Concurrency Chevron down icon Chevron up icon
7. Macros in Clojure Chevron down icon Chevron up icon
Index Chevron down icon Chevron up icon
Get free access to Packt library with over 7500+ books and video courses for 7 days!
Start Free Trial

FAQs

What is included in a Packt subscription? Chevron down icon Chevron up icon

A subscription provides you with full access to view all Packt and licnesed content online, this includes exclusive access to Early Access titles. Depending on the tier chosen you can also earn credits and discounts to use for owning content

How can I cancel my subscription? Chevron down icon Chevron up icon

To cancel your subscription with us simply go to the account page - found in the top right of the page or at https://subscription.packtpub.com/my-account/subscription - From here you will see the ‘cancel subscription’ button in the grey box with your subscription information in.

What are credits? Chevron down icon Chevron up icon

Credits can be earned from reading 40 section of any title within the payment cycle - a month starting from the day of subscription payment. You also earn a Credit every month if you subscribe to our annual or 18 month plans. Credits can be used to buy books DRM free, the same way that you would pay for a book. Your credits can be found in the subscription homepage - subscription.packtpub.com - clicking on ‘the my’ library dropdown and selecting ‘credits’.

What happens if an Early Access Course is cancelled? Chevron down icon Chevron up icon

Projects are rarely cancelled, but sometimes it's unavoidable. If an Early Access course is cancelled or excessively delayed, you can exchange your purchase for another course. For further details, please contact us here.

Where can I send feedback about an Early Access title? Chevron down icon Chevron up icon

If you have any feedback about the product you're reading, or Early Access in general, then please fill out a contact form here and we'll make sure the feedback gets to the right team. 

Can I download the code files for Early Access titles? Chevron down icon Chevron up icon

We try to ensure that all books in Early Access have code available to use, download, and fork on GitHub. This helps us be more agile in the development of the book, and helps keep the often changing code base of new versions and new technologies as up to date as possible. Unfortunately, however, there will be rare cases when it is not possible for us to have downloadable code samples available until publication.

When we publish the book, the code files will also be available to download from the Packt website.

How accurate is the publication date? Chevron down icon Chevron up icon

The publication date is as accurate as we can be at any point in the project. Unfortunately, delays can happen. Often those delays are out of our control, such as changes to the technology code base or delays in the tech release. We do our best to give you an accurate estimate of the publication date at any given time, and as more chapters are delivered, the more accurate the delivery date will become.

How will I know when new chapters are ready? Chevron down icon Chevron up icon

We'll let you know every time there has been an update to a course that you've bought in Early Access. You'll get an email to let you know there has been a new chapter, or a change to a previous chapter. The new chapters are automatically added to your account, so you can also check back there any time you're ready and download or read them online.

I am a Packt subscriber, do I get Early Access? Chevron down icon Chevron up icon

Yes, all Early Access content is fully available through your subscription. You will need to have a paid for or active trial subscription in order to access all titles.

How is Early Access delivered? Chevron down icon Chevron up icon

Early Access is currently only available as a PDF or through our online reader. As we make changes or add new chapters, the files in your Packt account will be updated so you can download them again or view them online immediately.

How do I buy Early Access content? Chevron down icon Chevron up icon

Early Access is a way of us getting our content to you quicker, but the method of buying the Early Access course is still the same. Just find the course you want to buy, go through the check-out steps, and you’ll get a confirmation email from us with information and a link to the relevant Early Access courses.

What is Early Access? Chevron down icon Chevron up icon

Keeping up to date with the latest technology is difficult; new versions, new frameworks, new techniques. This feature gives you a head-start to our content, as it's being created. With Early Access you'll receive each chapter as it's written, and get regular updates throughout the product's development, as well as the final course as soon as it's ready.We created Early Access as a means of giving you the information you need, as soon as it's available. As we go through the process of developing a course, 99% of it can be ready but we can't publish until that last 1% falls in to place. Early Access helps to unlock the potential of our content early, to help you start your learning when you need it most. You not only get access to every chapter as it's delivered, edited, and updated, but you'll also get the finalized, DRM-free product to download in any format you want when it's published. As a member of Packt, you'll also be eligible for our exclusive offers, including a free course every day, and discounts on new and popular titles.

Modal Close icon
Modal Close icon