On 09/10/2012 06:17 PM, Vincent Massol wrote:
With this finding writing a macro requires between 5 to 6 Classes:
* DefaultContentDescriptor (only if there's content)
* XXXMacroParameters
* List
* Block
* MacroTransformationContext
* MacroExecutionException
Our checkstyle config fails above 20 which means Macro classes have about 14
additional deps on external classes allowed before they break. Which should
normally be more than enough.
My understanding is that reading the code is hard when there are too many
references to external classes (incidentally it also makes the code more
brittle as there are more chances it'll break due to an issue with the used
classes). Apparently 7 (+/- 2) is the magic number (see
http://en.wikipedia.org/wiki/The_Magical_Number_Seven,_Plus_or_Minus_Two)
So this shows "20" was magic to begin with. How do you go from 7 +/-2 to
20 ?
I find it a bit specious to apply the theories exposed in the article to
a program's class external classes without a pinch of salt. It would be
saying their is a good match between the notion of "object" as described
in the experiments (so in the sense of an item of input, like a word in
a list of words or a sound in a list of distinct sounds) and the notion
of a class of objects in programming.
What I'm trying to say is that maybe we should rather accept the fact 20
is magic to begin with and try and figure out if this works for us and
tweak it if necessary - rather than trying to rationalize it with
bridges to psychology thesis that are far from obvious (not that the
thesis don't apply to programming ; just that the impendance of an
"input" or "unit of thought" is IMHO not so easy to match with
programming concepts without making blind guesses). Maybe I'm wrong,
it's just I find this kind of rationalization somehow naïve.
Hope that made sense.
Also, a note about ignoring classes that "don't require effort to
understand" (or to look at their source code), they would probably span
more than "standard Java classes" like Collections, no ? For example,
what about common-langs (StringUtils, etc.) ?
Jerome
So IMO we have 2 options that could make sense (ie we can rationalize them):
* Keep this default value of 20 total which includes some standard JDK classes.
14 deps for Macro should be enough, even if we count, say 2-4 more for standard
Java classes like Collection classes.That still gives us about 10 deps for
additional XWiki classes.
* Decide to exclude some classes that are basically part of the Java language
(such as Collection classes) since they don't increase the reading complexity
of the code since everyone knows what they do and we don't need to look their
source code or doc to understand them. However, if we do so then we should
reduce the allowed Fan out to 7 (+/- 2) so let's say to 9. So that gives us
only 9 deps for XWiki classes, compared to about 15 ATM...
IMO the second option is much harder for us than the first one and that's why
I'd keep the first option...
BTW the reason I wrote about all this is because I made a change to the
ChartMacro and the fan out became 21… In the end I refactored the code and got
a slightly better design (and fixed a bug at the same time…).
Thanks
-Vincent
On Sep 10, 2012, at 4:59 PM, Vincent Massol <[email protected]> wrote:
Hi devs,
I wanted to understand how Checkstyle computes the Class Fan out so I debugged
it.
Here are my findings:
* Some classes are excluded by default:
mIgnoredClassNames.add("boolean");
mIgnoredClassNames.add("byte");
mIgnoredClassNames.add("char");
mIgnoredClassNames.add("double");
mIgnoredClassNames.add("float");
mIgnoredClassNames.add("int");
mIgnoredClassNames.add("long");
mIgnoredClassNames.add("short");
mIgnoredClassNames.add("void");
mIgnoredClassNames.add("Boolean");
mIgnoredClassNames.add("Byte");
mIgnoredClassNames.add("Character");
mIgnoredClassNames.add("Double");
mIgnoredClassNames.add("Float");
mIgnoredClassNames.add("Integer");
mIgnoredClassNames.add("Long");
mIgnoredClassNames.add("Object");
mIgnoredClassNames.add("Short");
mIgnoredClassNames.add("String");
mIgnoredClassNames.add("StringBuffer");
mIgnoredClassNames.add("Void");
mIgnoredClassNames.add("ArrayIndexOutOfBoundsException");
mIgnoredClassNames.add("Exception");
mIgnoredClassNames.add("RuntimeException");
mIgnoredClassNames.add("IllegalArgumentException");
mIgnoredClassNames.add("IllegalStateException");
mIgnoredClassNames.add("IndexOutOfBoundsException");
mIgnoredClassNames.add("NullPointerException");
mIgnoredClassNames.add("Throwable");
mIgnoredClassNames.add("SecurityException");
mIgnoredClassNames.add("UnsupportedOperationException");
* All classes in java.lang.* are excluded too
* Annotation classes are not counted
* Classes in the same package are counted (they won't appear in import since
it's in the same package so don't count imports to get class fan out)
* Static method calls are not counted. So for example StringUtils from Commons
Lang never counts for class Fan out
* Enums are not counted (no new XXX() done. That's why static method calls are
not counted too BTW)
* Classes used in class extend or implement are not counted too.
Hope it helps
-Vincent
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--
Peace,
—Jerome
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