The Author’s Inside Guide to Reading Eclipse Collections Categorically
TL;DR — Read Chapters 1, 2, 3. Jump to 11. Skim 4–10. Dive in as desired.
The book, Eclipse Collections Categorically, will continue to be available to Kindle Unlimited subscribers until October 12, 2025.
The book is also available to purchase in print versions at Amazon and Barnes & Noble.
This blog can help readers determine the best options for reading the book given time constraints.
How to learn a feature-rich API
Eclipse Collections Categorically overcomes the challenge of learning and comprehending a feature-rich API by grouping the methods into method categories. This was an innovative information chunking technique I learned from the classic Smalltalk programming language in the 1990s. What the book doesn’t tell you is how to go about reading it to maximize your reading and learning style given constraints on your time.
The book can be read as a story or as a reference guide.
At 429 pages in paperback, and 377 pages in the larger hardcover book, it can take a while to read the whole book. The good news is that the book was designed to be read end-to-end or be picked up and read at any point as a reference. The decision of how best to read the book is up to the reader.
1. Read the Preface
The Preface is the story of where, why, and how Eclipse Collections was developed. It is an important backstory, if you want to understand what drove me to create an open source Java collections library that needed lambdas, a decade before lambdas arrived in Java, and then write a book about it two decades later.
**The Preface is free to read in the online reading sample at Amazon.
2. Read the Introduction and THIS section
The Introduction tells you how the book is organized. This will help inform you as how and where you want to spend your time. The rest of the Introduction tells you how to acquire Eclipse Collections and access the source. There is a new GitHub project that does that as well, and has the added benefit of including the latest version of Eclipse Collections (13.0) that was released at the end of June, 2025.
**The Introduction is free to read in the online reading sample at Amazon.
New GitHub Repository with additional resources
The following GitHub project can be used as a hand-on resource to follow along with the code examples in the book. Some folks learn best by doing. This repository was created after the book was published. There is a Maven project and a sample of the examples from the book that can be run, since they are executable tests.
There are two code examples per chapter shared in this repo (it is only a sample), but the project is setup and includes the dependencies needed to personally explore and try any of the examples in the book.
3. Decide how you want to read the book
The manner in which you decide to read the book depends on what you are looking to get out of it. Once you understand how the book is organized in the Introduction, your decision on how to approach reading the book should become clearer.
Now that there is a GitHub repo with resources to accompany the book, it will be easier to take a hands-on approach for some folks who like to experiment and see code run. The code examples in the book are effectively the solutions to a code kata, which is focused on learning the Eclipse Collections API in a comprehensive manner.
Option A: Read from Beginning to End
The chapters in Eclipse Collections Categorically are organized by method categories. The chapters are ordered specifically to help developers new to Eclipse Collections build skills and understanding in an incremental fashion. There is a story that builds upon previous chapters as the reader progresses.
I wanted to write a story that could be read from beginning to end. Depending on the speed you read and the time you have to focus, this can take the average reader a while.
If you are time-constrained and just want to learn some of the big ideas covered in the book, then I would suggest Option B to start your journey.
Option B: Read Chapters 1, 2, 3. Jump to 11. Skim 4–10.
Chapters 1, 2, 3 and give you all that you need to get started on a journey of learning Eclipse Collections, using method categories as an indexed guide (aka, Categorically). Chapter 11 is the summary chapter for the book. Chapter 11 shows you the symmetry that exists in the library, and how it can aid your learning as you use Eclipse Collections in your projects.
Chapter 3 takes you on a journey through a straightforward but surprising method category — counting. I recommend reading Chapter 3 from beginning to end as it will help you understand the symmetry of chapters 4 through 10.
Chapters 4–10 cover additional method categories (testing, finding, filtering, transforming, etc.). You can read them straight through or jump around them in any order. One option that someone has shared with me that worked well for them was to skim chapters 4 through 10 to see what was in them, and then go back and focus on particular sections when you want more detail on various methods. Chapters 3–10 will help you learn different techniques for accomplishing things with the Eclipse Collections API. They are an efficient index into the 134 methods you can see in the diagrams in the image above.
4. The Appendices
There is a lot of content in the appendices. I would suggest reading them in any order that interests you. There is a lot of interesting data, background, and some advice on using collections effectively in object-oriented domains in Java.
The Introduction covers what is in the appendices, so I won’t repeat it here.
Enjoy the book!
I hope you can take advantage of and enjoy the limited time free book promotion. If you have Kindle Unlimited, you have until October 12th, 2025. If you enjoy the book, I hope you will consider purchasing a print or digital copy and making it a permanent part of your physical or virtual bookshelf.
Thanks for reading, and enjoy!
I am the creator of and committer for the Eclipse Collections OSS project, which is managed at the Eclipse Foundation. Eclipse Collections is open for contributions. I am also the author of the book, Eclipse Collections Categorically: Level up your programming game.
