10 Sep
2012
10 Sep
'12
6:17 p.m.
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 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 <vincent(a)massol.net> 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