On 09/10/2012 07:23 PM, Vincent Massol wrote:
Hi Jerome,
Hey I didn't really want to awaken this topic again ;) I already gave my
opinion on the other thread (I still need to reply to Sergiu's last mail BTW).
I just wanted to explain how checkstyle computes the class fan out and share
that since it was useful for me to fix one class fan out issue I had.
See below.
On Sep 10, 2012, at 7:06 PM, Jerome Velociter <[email protected]> wrote:
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 ?
Would be interesting to ask the checkstyle guy why they picked this value. My
guess is that they used something like 7 + standard java classes.
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.
Not my choice. All references to Class Fan Out say that the default value
should be around 7 and quote this article.
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
I've already answered to this. I'm -1 to change what we have in a random manner
with another random value. What I said is to show me some code and we can
discuss on this basis.
Yes, this is a way better approach than trying to rationalize said
random numbers. That was exactly my point actually.
Jerome
Sergiu has pointed out some code but I didn't get the time to look at it yet.
I need to do that and if the outcome is that we can't make it pass with a good
design then we can discuss either make an exclude for this special case or
decide that the case is generic.
- 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.
Well, there's not much point in saying that something is wrong if you don't
provide an alternative… If you're going against the established standard then
you better be an expert in the domain. I know I'm not. But even if we agree
that the study has no meaning, it doesn't change the fact that to change what
we have we need to have a good reason to do so and we need to define the new
value while still ensuring that the check still makes 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 ?
Yep, I mentioned that in my mail (I said "Collection" classes).
For example, what about common-langs (StringUtils, etc.) ?
I wouldn't put those, not everyone know them and again static method calls
**don't count** for the class fan out …
Anyway ATM I don't agree about starting to ignore classes without at least one
good example where we have to do so to make the fan out check pass.
I write new code almost everyday and it's seldom that I have issues with class
fan out and most of the time when it happens it's because I've been lazy and I
can fix the issue in a few minutes. This makes me think that the current value
is good. As I've already said in the other thread for me it would be much
better to agree to do a checkstyle exclude of *only* the ClassFanOut check for
a given class rather than change the default for everyone.
Thanks
-Vincent
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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