Dean Wampler - Functional Programming for Java Developers

Copyright 2011 Dean Wampler

OReilly books may be purchased for educational, business, or sales promotional use. Online editions are also available for most titles (.

Nutshell Handbook, the Nutshell Handbook logo, and the OReilly logo are registered trademarks of OReilly Media, Inc. Functional Programming for Java Developers , the image of a pronghorn antelope, and related trade dress are trademarks of OReilly Media, Inc.

Many of the designations used by manufacturers and sellers to distinguish their products are claimed as trademarks. Where those designations appear in this book, and OReilly Media, Inc., was aware of a trademark claim, the designations have been printed in caps or initial caps.

While every precaution has been taken in the preparation of this book, the publisher and authors assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein.

Why should a Java developer learn about functional programming (FP)? After all, hasnt functional programming been safely hidden in academia for decades? Isnt object- oriented programming (OOP) all we really need? This book explains why functional programming has become an important tool for the challenges of our time and how you, a Java developer, can use it to your advantage.

) is difficult to do well and few developers are good at it. As well see, functional programming offers better strategies for writing robust, concurrent software.

An example of the greater need for horizontal scalability is the growth of massive data sets requiring management and analysis, the so-called big data trend. These are data sets that are too large for traditional database management systems. They require clusters of computers to store and process the data. Today, its not just Google, Yahoo!, Facebook, and Twitter who work with big data. Many organizations face this challenge.

(OReilly). Scala is a JVM language, a potential successor to Java, with the goal of bringing object-oriented and functional programming into one coherent whole. Clojure is the other well-known functional language on the JVM. It is a Lisp dialect that minimizes the use of OOP in favor of functional programming. Clojure embodies a powerful vision for how programming should be done.

Fortunately, you dont have to adopt a new language to enjoy many of the benefits of functional programming. Back in early 1990s, I used an object-oriented approach in the C software I wrote, until I could use C++. Similarly, if youre working with an object-oriented language, like Java, you can still apply many of the ideas from functional programming.

Unfortunately, much of the literature on functional programming is difficult to understand for people who are new to it. This short book offers a pragmatic, approachable introduction to functional programming. While aimed at the Java developer, the principles are general and will benefit anyone familiar with an object-oriented language.

I assume that you are well versed in object-oriented programming and you can read Java code. Youll find some exercises at the end of each chapter to help you practice and expand on what youve learned.

Because this is a short introduction and because it is difficult to represent some functional concepts in Java, there will be several topics that I wont discuss in the text, although I have added glossary entries, for completeness. These topics include currying , partial application , and comprehensions . Ill briefly discuss several other topics, such as combinators , laziness , and monads , to give you a taste of their importance. However, fully understanding these topics isnt necessary when youre new to functional programming.

I hope you find functional programming as seductive as I did. Let me know how it goes!

You can learn more at the books catalog page (http://oreilly.com/catalog/9781449311032/).

The following typographical conventions are used in this book: