Clojure for Java Developers

Eduardo Diaz

• Publisher: Packt Publishing
• Year: 2016
• eBook ISBN: 9781785281501
• Edition: 1
• Topic: Computer Science
• Subtopic: Programming in Java
• Index: Computer Science

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

About This Book

• 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

Who This Book Is 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

In Detail

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.

Style and approach

An easy to follow, step-by-step, guide on how to start writing Clojure programs making use of all of its varied features and advantages. As this is a new language, certain new concepts are supported with theoretical section followed by simple projects to help you gain a better understanding and practice of how Clojure works.

Clojure for Java Developers

---

Table of Contents

Clojure for Java Developers

Credits

About the Author

About the Reviewer

www.PacktPub.com

eBooks, discount offers, and more

Why subscribe?

Preface

What this book covers

What you need for this book

Who this book is for

Conventions

Reader feedback

Customer support

Downloading the example code

Downloading the color images of this book

Piracy

Questions

1. Getting Started with Clojure

Getting to know Clojure

Installing Leiningen

Using a REPL

The nREPL protocol

Hello world

REPL utilities and conventions

Creating a new project

Project structure

Creating a standalone app

Using Cursive Clojure

Installing Cursive Clojure

Getting started with Clojure code and data

Lists in Clojure

Operations in Clojure

Functions in Clojure

Clojure's data types

Scalars

Collection data types

Summary

2. Namespaces, Packages, and Tests

Namespaces in Clojure

Packages in Clojure

The classpath and the classloader

Back to Clojure namespaces

Playing with namespaces

Creating a new namespace

Working with namespaces on the REPL

Testing in Clojure

Testing from the command line

Testing in IntelliJ

Summary

3. Interacting with Java

Using Maven dependencies

Clojure interop syntax

Creating an object

Calling an instance method

Calling a static method or function

Accessing inner classes

Writing a simple image namespace

Writing the tests

The let statement

Destructuring in Clojure

Sequential destructuring

Associative destructuring

Exposing your code to Java

Testing from Groovy

Proxy and reify

Summary

4. Collections and Functional Programming

Basics of functional programming

Persistent collections

Types of collections in Clojure

The sequence abstraction

Specific collection types in Clojure

Vectors

Lists

Maps

Sorted maps and hash maps

Common properties

Sets

Sorted sets and hash sets

Common properties

Union, difference, and intersection

Applying functional programming to collections

The imperative programming model

The functional paradigm

Functional programming and immutability

Laziness

Summary

5. Multimethods and Protocols

Polymorphism in Java

Multimethods in Clojure

Keyword hierarchies

isa?

parents

descendants

underive

A la carte dispatch functions

Protocols in Clojure

Records in Clojure

Summary

6. Concurrency

Using your Java knowledge

The Clojure model of state and identity

Promises

Pulsar and lightweight threads

Futures

Software transactional memory and refs

Atoms

Agents

Validators

Watchers

core.async

Why lightweight threads?

Goblocks

Channels

Transducers

Summary

7. Macros in Clojure

Lisp's foundational ideas

Macros as code modification tools

Modifying code in Java

Modifying code in Groovy

The @ToString annotation

The @TupleConstructor annotation

The @Slf4j annotation

Writing your first macro

Debugging your first macro

Quote, syntax quote, and unquoting

Unquote splicing

gensym

Macros in the real world

References

Summary

Index

Clojure for Java Developers

Copyright © 2016 Packt Publishing

All rights reserved. No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, without the prior written permission of the publisher, except in the case of brief quotations embedded in critical articles or reviews.

Every effort has been made in the preparation of this book to ensure the accuracy of the information presented. However, the information contained in this book is sold without warranty, either express or implied. Neither the author, nor Packt Publishing, and its dealers and distributors will be held liable for any damages caused or alleged to be caused directly or indirectly by this book.

Packt Publishing has endeavored to provide trademark information about all of the companies and products mentioned in this book by the appropriate use of capitals. However, Packt Publishing cannot guarantee the accuracy of this information.

First published: February 2016

Production reference: 1190216

Published by Packt Publishing Ltd.

Livery Place

35 Livery Street

Birmingham B3 2PB, UK.

ISBN 978-1-78528-150-1

www.packtpub.com

Credits

Author

Eduardo Díaz

Reviewers

Ning Sun

Nate West

Commissioning Editor

Kunal Parikh

Acquisition Editor

Usha Iyer

Content Development Editors

Neeshma Ramakrishnan

Kajal Thapar

Technical Editor

Saurabh Malhotra

Copy Editor

Sneha Singh

Project Coordinator

Shweta H. Birwatkar

Proofreaders

Safis Editing

Indexer

Hemangini Bari

Production Coordinator

Shantanu N. Zagade

Cover Work

Shantanu N. Zagade

About the Author

Eduardo Díaz is a developer with a strong background in the Java language. He has a passion for functional programming and new programming paradigms. His work includes full stack development, systems design, and high volume real time data processing.

He has worked on every technology related problem you can imagine, as a consultant solving anything related to Java, UNIX, C, or any other strange problem you might have had.

As a developer, he has been working for around 10 years on Java, Python, Scala, Clojure, in the media, bank, and primarily communications industries.

He is currently working at Grupo Expansion, a media company, where he helps design and implement a new content delivery platform aiming to empower content editors and encourage developers to find new ways to use data.

First of all, I would like to thank Neeshma Ramakrishnan and Kajal Thapar at Packt Publishing, they are the best editors, they have an incredible amount of patience and wi...

Table of contents

• Clojure for Java Developers