Hi devs,
Short version:
I'd like to increase the allowed maximum value for the Class Fan-Out
Complexity checkstyle rule from 20 to 25, since a bare component already
uses 1 to 4 imports, and the 20 rule was set before we had components.
Long version:
The Class Fan-Out Complexity metric measures how many other classes are
used by a class. Keeping this to a small value is a good goal, since it
favors loose-coupling, small and independent classes, and makes it
harder to put more than one responsibility in a single class.
However, there are several problems:
One is that this counts utility classes and interfaces, such as
java.util.List, and a fairly complex class uses more than one such
utility class; they usually come in pairs (the interface and the
implementation). And more and more classes are using apache-commons
utilities like StringUtils or IOUtils, which are just shortcut helper
methods that could be implemented in a few lines of code, so we're
trading one import for reduced code complexity, which is a good thing,
even though apparently it's increasing the Fan-Out measure.
Another is that a bare Initializable component implementation will import:
- its component role interface
- Initializable and InitializationException
- Logger
And since good libraries also follow the "many small classes" paradigm,
barely using some of our dependencies will add a lot of imports. For
example, the LucenePlugin has 25 org.apache.lucene.* imports just for
initializing the server and sending search requests.
While the current maximum, 20, is enough for the majority of our classes
and interfaces, I've found myself often enough trying to refactor a
class to get down from 23 or even 21 imports, and usually I find myself
doing ugly tricks, keeping the actual code complexity the same or even
worse. Best case is that I extract an extra class that just contains the
non-public utility methods that were initially in the component
implementation, but that class is meaningless out of the context of its
parent class, so that is also a bad decision, IMHO.
So, I propose to increase the Fan-Out limit to 25, while keeping the
requirement that classes should be kept as small as possible.
--
Sergiu Dumitriu
http://purl.org/net/sergiu/
_______________________________________________
devs mailing list
[email protected]
http://lists.xwiki.org/mailman/listinfo/devs
