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APIs And What Not To Do

04.14.2010
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APIs seem to be like opinions. Everyone has one, and no two people have the same concept of what constitutes a good one. An API is supposed to be an interface that is exposed for other programs or programmers to use to interact with your code. Except, each API, like an individual, is unique with its own flaws and niceties. A great API is one which reduces the amount of code you have to write when you use it. I personally feel amazing if I can get something done with minimal code. That just screams “GOOD API” to me.

On the other hand, a bad API leaves you feeling dirty, unclean even, as if you are committing grave sins against nature even by just using it. Here are a few common mistakes which end up leaving that bad taste in your mouth (with examples, of course!) :

Bad APIs

These are the worst offenders, the APIs which are supposedly there to make your life easier, but just end up making it more work to use it than rewriting it from scratch. I faced one of the bigger offenders of this one recently when I was working with GWT. I was trying to create a tree structure to represent a navigation hierarchy when it dawned on me.

A GWT Tree is created by creating a Tree object, and then creating a tree item for each node. To append children to each node, you create further tree items and add whatever text or elements you want to it. So to summarize, even if I have a data structure to represent my tree (which in most cases, I do), I will have to traverse it manually, create tree items, tell each one how to render itself and then append it to the correct items. Yuck.

Now consider how JFace creates a Tree (which I consider much more powerful and a nicer API altogether). You create a TreeViewer, set its data source / input. Then, you set a content provider which knows how to traverse your data object and get children / parents. You can also set a LabelProvider which tells it how to render its data elements. End result? Nice clean code that I actually feel satisfied about.

Most of these are the end result of rushed / not well thought out design. Having a concrete use case prior to designing it should have been enough to scream out “Its ugly!!!”. Suggestion to prevent this : write a test / use case for anything you start designing, so you can get a feel for how it feels in action. That should help you avoid a lot of these.

Not fully thought out APIs

This one is similar to the previous one, but I think it deserves section and example of its own. This happens when you almost nail the API, but fail to consider some common uses of the API. The biggest offender of this one I believe is the Java List API.

The two most common use cases I have in Java when I work with lists are
1.) Iterating through them to perform some operation and
2.) Filtering the list to get a subset

The second operation is so common that I get annoyed now that I have to create an empty list, iterate through each one using a for each and conditionally add elements to the new list. Now I realize that Java doesn’t make it easy to pass in functions (check my older article about this) as arguments, but what I really really want here is the ability to do myList.filter(predicate) where predicate is a predicate function I decide, which returns the filtered list with elements matching the predicate.

There are many more such common operations missing on the List interface, but this is the most egregious one I believe. Javascript also gets this wrong, but underscore, a JS library adds a lot of this which makes working with lists and collections a dream.

Misnamed APIs and methods

How many times have you called a method, only to realize that it didn’t really do what you thought it did? Or look for a method XYZ, only to realize later that it had been named YXZ instead. Raise your hands if you have experienced this. For some reason, an apple for someone almost always turns out to be an orange for someone else.

I’ll switch to bashing on JS for this one, underscore in particular. For all the amazing methods that underscore provides in JS, they really have a problem with naming. I ended up looking for a collection.contains method, and ended up finding only indexOf, so I initially assumed that they didn’t have it. I mean, if I look for contains, at best, I will also look for has, hasKey. Browsing through the list of method names, I might have even accepted includes (though it would not have been my first choice). But never in all my life would I have expected it to be include (Yes, that is include, as in singular!). People, what were you thinking????

Liars

The final set of APIs which can annoy (but are easily worked around, just like the previous section) are APIs which lie. These include APIs which don’t do what the function name suggests it does (no obvious example from the open source land comes to mind, thankfully). The other kind is one which is not done with work even after the object is created. Most times, it is the case of a lurking init / initialize method. And if you ever see an interface called Initializable, run in the opposite direction.

From http://theshyam.com/2010/04/apis-and-what-not-to-do

Published at DZone with permission of its author, Shyam Seshadri.

(Note: Opinions expressed in this article and its replies are the opinions of their respective authors and not those of DZone, Inc.)

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Peter Arrenbrecht replied on Thu, 2010/04/15 - 4:57am

Suggestion to prevent this : write a test / use case for anything you start designing, so you can get a feel for how it feels in action.
You might be interested in taking this one step further and coupling it to your API docs. For Java in particular, I wrote a tool called JCite to cite use-case tests into the docs.

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