Practical API Design: Confessions of a Java Framework Architect is the book I've always been waiting for. Jaroslav Tulach, the founder and architect of NetBeans, created a highly recommend read for everyone in charge of developing APIs.
But even if it's not your job to define interfaces, you are somewhat alway on the other side consuming them and it's good to know what drives evolution of the APIs you work with.
The book consists of 3 parts:
Part 1 is called "Theory and Justification". It defines the terminology and background which gives you the necessary foundation to explain and justify API design.
Let me give you and example: Have you ever had problems explaining your design to a colleague? You couldn't find the right words to reasonably highlight your decision, but you know it was right? The only justification was your intuition and the feeling that your design was the right choice. Does that sound familiar?
That's where Part 1 of this book comes in and tries to give you a tool to justify and even measure the quality of your design decisions: Selective Cluelessness. It's a principle which is based on the assumption that you can achieve more by knowing less:
"The more good APIs we have, the bigger the systems we'll be able to build without understanding all their details."
"Practical Design" is Part 2 and basically puts the theory highlighted in the first part to practice. Using Java, the author provides a set of what he calls API design patterns. They are design patterns in the traditional sense, but with a focus on evolution. Most of them accompanied by an examples the NetBeans APIs. It doesn't matter if you are not familiar with NetBeans. Due to the author's years of experience with NetBeans, he does a great job explaining the problems it was facing and how they came with a solution, which evolved into an API design pattern.
..., it's slightly more complicated to design a universe than building a house. As a result, we need an enhanced version of the design patters. We need patterns that help us building a "universe".
Part 3 of the book, "Daily Life", is a collection of advices on how to bugfix, evolve and maintain an API. The author points out how important versioning is and how NetBeans solves such a problem. He highlights the importance of compatibility and how to keep the promises to the users of your APIs.
The theory and initial design are just the tip of the iceberg. The rest is the real work.
I'm really glad I read this book, although it took me quite a while. The reason is not the 365 pages. It was all the moments I had during reading it. So many times I was reminded of mistakes I made in APIs I previously designed. I often pondered on whether a solution suggested in the book was better than the one I came up with. I think that's what makes a book interesting, if it makes you think and critically review your own solutions.
I enjoyed taking the journey through the API universe and learning how to design an API in a selective cluelessness way. As for the reasons why you should read this book:
... when you understand the API world, its needs and its laws of evolution, you can shape it into a form containing all that the creators of the oldest and most perfect science always searched for - beauty, truth and elegance. A properly API universe ain't a bad place to be.