Provenance Jun 15, 2025 Origins of API Design Matters I started API Design Matters in early 2023 (if you’ve been reading since then, Thank You!), but the idea goes back much further. Back in the mid 90’s (yeah, I’ve been around a while…) I was deep into that new “Java thang”. In June 2025, Emmanuel Paraskakis shared slides from a 2007 talk Joshua Bloch had given, titled How to Design Good APIs, and Why it Matters. I had seen a version of this talk in my Java years at a conference, and I had the pleasure of working with Java API design experts like Josh Bloch and Doug Lea as they built out the Collection framework (lists, maps, etc) for Java 2 in the early days. The title of that talk lodged itself in the back of my brain, almost as much as the content of the talk, and both were a large part of why I created API Design Matters… and why I named it as I did. Josh and Doug and others were gracious and accepted a lot of input from the younger me, and answered my questions about the emerging design of Java’s Collection framework. Those conversations are lost to time, but I do remember their impact. A specific example I recall from the early Java Collection API design discussions centered on the collection interfaces’ isEmpty() query function, which returns true if the collection was empty (had no items), false if not. I asked about the need for such a function, since the collections already had a length() function. It seemed unnecessary to add a collection.isEmpty() method because a client could trivially use (collection.length() == 0). However, Josh kindly pointed out that, with so many different/possible collection implementations, the length() function may be expensive to compute. For example, for a linked list, computing linkedList.length() is O(n) (where n is the number of items in the list), not O(1), whereas the implementation of linkedList.isEmpty() function for a linked list is trivially O(1). While API composability is nice, it may come at the cost of performance. Many of the practices and pragmas Josh shared then, as well in his InfoQ article, “Bumper-Sticker API Design”, stuck with me because they also apply to Web API design. The one principle I have shared the most: Public APIs, like diamonds, are forever.” — Joshua Bloch When I worked at SAS, I shared an example of this principle several times when discussing API design. As late as 2017, I would show examples of small SAS programs from the 1976 SAS manual, and the programs continued to work unaltered in the SAS System of 2017. Backwards compatibility is as critical to the longevity of an API as it is to a programming language/platform. Josh also wrote: If there is a fundamental theorem of API design, this is it … Every facet of an API should be as small as possible, but no smaller. You can always add things later, but you can’t take them away. Minimizing conceptual weight is more important than class- or method-count. Obviously, design forces often oppose on another. The collection interface footprint would be smaller without an isEmpty() function, but the negative impact of omitting it is offset by the benefit of including it. Another important aspect of API Design Matters provenance that I wish to share is that none of the text in API Design Matters was generated by AI. (I did try AI for one image and I doubt I’ll do that again because the result was so awful). But I have never used an AI to draft, write, or rewrite my posts—It’s all me. It always will be. I wish to acknowledge and thank Josh Bloch and Doug Lea and others who taught me so much. Who has inspired your work with APIs? Let me know in the comments. Join the discussion Note: This article was originally published on the auhor’s API Design Matters Substack.