Kevlin Henney - 97 Things Every Java Programmer Should Know: Collective Wisdom from the Experts

by Kevlin Henney and Trisha Gee

Copyright 2020 OReilly Media Inc. All rights reserved.

Printed in the United States of America.

Published by OReilly Media, Inc., 1005 Gravenstein Highway North, Sebastopol, CA 95472.

OReilly books may be purchased for educational, business, or sales promotional use. Online editions are also available for most titles (http://oreilly.com). For more information, contact our corporate/institutional sales department: 800-998-9938 or corporate@oreilly.com .

• Acquisitions Editor: Suzanne McQuade
• Developmental Editor: Corbin Collins
• Production Editor: Beth Kelly
• Copyeditor: Piper Editorial
• Proofreader: Sonia Saruba
• Indexer: Ellen Troutman-Zaig
• Interior Designer: David Futato
• Cover Designer: Karen Montgomery
• Illustrator: Rebecca Demarest

• June 2020: First Edition

See http://oreilly.com/catalog/errata.csp?isbn=9781491952696 for release details.

The OReilly logo is a registered trademark of OReilly Media, Inc. 97 Things Every Java Programmer Should Know, the cover image, and related trade dress are trademarks of OReilly Media, Inc.

The views expressed in this work are those of the authors, and do not represent the publishers views. While the publisher and the authors have used good faith efforts to ensure that the information and instructions contained in this work are accurate, the publisher and the authors disclaim all responsibility for errors or omissions, including without limitation responsibility for damages resulting from the use of or reliance on this work. Use of the information and instructions contained in this work is at your own risk. If any code samples or other technology this work contains or describes is subject to open source licenses or the intellectual property rights of others, it is your responsibility to ensure that your use thereof complies with such licenses and/or rights.

978-1-491-95269-6

[LSI]

To the memory of those who shaped us
through their wisdom and compassion

Preface

The mind is not a vessel that needs filling, but wood that needs igniting.

Plutarch

What should every Java programmer know? It depends. It depends on who you ask, why you ask, and when you ask. There are at least as many suggestions as there are points of view. In a language, platform, ecosystem, and community that affects the software and lives of so many people, and has done so from one century to the next, from one core to many, from megabytes to gigabytes, it depends on more than you could ever hope to cover in a single book by a single author.

Instead, in this book, we draw on some of those many perspectives to collect together for you a cross section and representation of the thinking in the Java-verse. Its not every thing, but it is 97 of them from 73 contributors. To quote the preface of 97 Things Every Programmer Should Know (OReilly):

With so much to know, so much to do, and so many ways of doing so, no single person or single source can lay claim to the one true way. The contributions do not dovetail like modular parts, and there is no intent that they shouldif anything, the opposite is true. The value of each contribution comes from its distinctiveness. The value of the collection lies in how the contributions complement, confirm, and even contradict one another. There is no overarching narrative: it is for you to respond to, reflect on, and connect together what you read, weighing it against your own context, knowledge, and experience.

What should every Java programmer know? In the 97 things we have sampled, the answers span the language, the JVM, testing techniques, the JDK, community, history, agile thinking, implementation know-how, professionalism, style, substance, programming paradigms, programmers as people, software architecture, skills beyond code, tooling, GC mechanics, non-Java JVM languagesand more.

Permissions

In the spirit of the first 97 Things books, each contribution in this volume follows a nonrestrictive, open source model. Each contribution is licensed under a Creative Commons Attribution 4.0 license. Many of the contributions also first appeared in the 97 Things Medium publication.

All these things are fuel and fire for your thoughts and your code.

OReilly Online Learning

Note

For more than 40 years, OReilly Media has provided technology and business training, knowledge, and insight to help companies succeed.

Our unique network of experts and innovators share their knowledge and expertise through books, articles, and our online learning platform. OReillys online learning platform gives you on-demand access to live training courses, in-depth learning paths, interactive coding environments, and a vast collection of text and video from OReilly and 200+ other publishers. For more information, visit http://oreilly.com.

How to Contact Us

Please address comments and questions concerning this book to the publisher:

• OReilly Media, Inc.
• 1005 Gravenstein Highway North
• Sebastopol, CA 95472
• 800-998-9938 (in the United States or Canada)
• 707-829-0515 (international or local)
• 707-829-0104 (fax)

We have a web page for this book, where we list errata, examples, and any additional information. You can access this page at https://oreil.ly/97Tejpsk.

Email to comment or ask technical questions about this book.

Visit http://oreilly.com for news and information about our books and courses.

Find us on Facebook: http://facebook.com/oreilly.

Follow us on Twitter at http://twitter.com/oreillymedia, and also check out http://twitter.com/97_Things.

Watch us on YouTube: http://youtube.com/oreillymedia.

Acknowledgments

Many people have contributed their time and their insight, both directly and indirectly, to the 97 Things Every Java Programmer Should Know project. They all deserve credit.

We would like to thank all those who took the time and effort to contribute to this book. We are also grateful for the additional feedback, comments, and suggestions provided by Brian Goetz.

Thanks to OReilly for the support they have provided for this project, including Zan McQuade and Corbin Collins for their guidance and for nurturing contributors and content, and Rachel Roumeliotis, Susan Conant, and Mike Loukides for their contributions on this journey.

Kevlin would also like to thank his wife, Carolyn, for making sense of his nonsense, and his sons, Stefan and Yannick, for making sense of their parents.

Trisha would like to add thanks to her husband, Isra, for helping her to see that stressing about not doing enough was not helping her to do anything, and her daughters, Evie and Amy, for providing unconditional love and cuddles.

We hope this book will be informative, insightful, and inspirational.

Enjoy!

Chapter 1. All You Need Is Java

Anders Nors