com.puppycrawl.tools.checkstyle.meta.checks.metrics.NPathComplexityCheck.xml Maven / Gradle / Ivy

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<?xml version="1.0" encoding="UTF-8"?>
<checkstyle-metadata>
   <module>
      <check fully-qualified-name="com.puppycrawl.tools.checkstyle.checks.metrics.NPathComplexityCheck"
             name="NPathComplexity"
             parent="com.puppycrawl.tools.checkstyle.TreeWalker">
         <description>&lt;p&gt;
 Checks the NPATH complexity against a specified limit.
 &lt;/p&gt;
 &lt;p&gt;
 The NPATH metric computes the number of possible execution paths through a
 function(method). It takes into account the nesting of conditional statements
 and multi-part boolean expressions (A &amp;amp;&amp;amp; B, C || D, E ? F :G and
 their combinations).
 &lt;/p&gt;
 &lt;p&gt;
 The NPATH metric was designed base on Cyclomatic complexity to avoid problem
 of Cyclomatic complexity metric like nesting level within a function(method).
 &lt;/p&gt;
 &lt;p&gt;
 Metric was described at &lt;a href="http://dl.acm.org/citation.cfm?id=42379"&gt;
 "NPATH: a measure of execution pathcomplexity and its applications"&lt;/a&gt;.
 If you need detailed description of algorithm, please read that article,
 it is well written and have number of examples and details.
 &lt;/p&gt;
 &lt;p&gt;
 Here is some quotes:
 &lt;/p&gt;
 &lt;blockquote&gt;
 An NPATH threshold value of 200 has been established for a function.
 The value 200 is based on studies done at AT&amp;amp;T Bell Laboratories [1988 year].
 &lt;/blockquote&gt;
 &lt;blockquote&gt;
 Some of the most effective methods of reducing the NPATH value include:
 &lt;ul&gt;
 &lt;li&gt;
 distributing functionality;
 &lt;/li&gt;
 &lt;li&gt;
 implementing multiple if statements as a switch statement;
 &lt;/li&gt;
 &lt;li&gt;
 creating a separate function for logical expressions with a high count of
 variables and (&amp;amp;&amp;amp;) and or (||) operators.
 &lt;/li&gt;
 &lt;/ul&gt;
 &lt;/blockquote&gt;
 &lt;blockquote&gt;
 Although strategies to reduce the NPATH complexity of functions are important,
 care must be taken not to distort the logical clarity of the software by
 applying a strategy to reduce the complexity of functions. That is, there is
 a point of diminishing return beyond which a further attempt at reduction of
 complexity distorts the logical clarity of the system structure.
 &lt;/blockquote&gt;
 &lt;table&gt;
 &lt;caption&gt;Examples&lt;/caption&gt;
 &lt;thead&gt;&lt;tr&gt;&lt;th&gt;Structure&lt;/th&gt;&lt;th&gt;Complexity expression&lt;/th&gt;&lt;/tr&gt;&lt;/thead&gt;
 &lt;tr&gt;&lt;td&gt;if ([expr]) { [if-range] }&lt;/td&gt;&lt;td&gt;NP(if-range) + 1 + NP(expr)&lt;/td&gt;&lt;/tr&gt;
 &lt;tr&gt;&lt;td&gt;if ([expr]) { [if-range] } else { [else-range] }&lt;/td&gt;
 &lt;td&gt;NP(if-range)+ NP(else-range) + NP(expr)&lt;/td&gt;&lt;/tr&gt;
 &lt;tr&gt;&lt;td&gt;while ([expr]) { [while-range] }&lt;/td&gt;&lt;td&gt;NP(while-range) + NP(expr) + 1&lt;/td&gt;&lt;/tr&gt;
 &lt;tr&gt;&lt;td&gt;do { [do-range] } while ([expr])&lt;/td&gt;&lt;td&gt;NP(do-range) + NP(expr) + 1&lt;/td&gt;&lt;/tr&gt;
 &lt;tr&gt;&lt;td&gt;for([expr1]; [expr2]; [expr3]) { [for-range] }&lt;/td&gt;
 &lt;td&gt;NP(for-range) + NP(expr1)+ NP(expr2) + NP(expr3) + 1&lt;/td&gt;&lt;/tr&gt;
 &lt;tr&gt;&lt;td&gt;switch ([expr]) { case : [case-range] default: [default-range] }&lt;/td&gt;
 &lt;td&gt;S(i=1:i=n)NP(case-range[i]) + NP(default-range) + NP(expr)&lt;/td&gt;&lt;/tr&gt;
 &lt;tr&gt;&lt;td&gt;[expr1] ? [expr2] : [expr3]&lt;/td&gt;&lt;td&gt;NP(expr1) + NP(expr2) + NP(expr3) + 2&lt;/td&gt;&lt;/tr&gt;
 &lt;tr&gt;&lt;td&gt;goto label&lt;/td&gt;&lt;td&gt;1&lt;/td&gt;&lt;/tr&gt;&lt;tr&gt;&lt;td&gt;break&lt;/td&gt;&lt;td&gt;1&lt;/td&gt;&lt;/tr&gt;
 &lt;tr&gt;&lt;td&gt;Expressions&lt;/td&gt;
 &lt;td&gt;Number of &amp;amp;&amp;amp; and || operators in expression. No operators - 0&lt;/td&gt;&lt;/tr&gt;
 &lt;tr&gt;&lt;td&gt;continue&lt;/td&gt;&lt;td&gt;1&lt;/td&gt;&lt;/tr&gt;&lt;tr&gt;&lt;td&gt;return&lt;/td&gt;&lt;td&gt;1&lt;/td&gt;&lt;/tr&gt;
 &lt;tr&gt;&lt;td&gt;Statement (even sequential statements)&lt;/td&gt;&lt;td&gt;1&lt;/td&gt;&lt;/tr&gt;
 &lt;tr&gt;&lt;td&gt;Empty block {}&lt;/td&gt;&lt;td&gt;1&lt;/td&gt;&lt;/tr&gt;&lt;tr&gt;&lt;td&gt;Function call&lt;/td&gt;&lt;td&gt;1&lt;/td&gt;
 &lt;/tr&gt;&lt;tr&gt;&lt;td&gt;Function(Method) declaration or Block&lt;/td&gt;&lt;td&gt;P(i=1:i=N)NP(Statement[i])&lt;/td&gt;&lt;/tr&gt;
 &lt;/table&gt;
 &lt;p&gt;
 &lt;b&gt;Rationale:&lt;/b&gt; Nejmeh says that his group had an informal NPATH limit of
 200 on individual routines; functions(methods) that exceeded this value were
 candidates for further decomposition - or at least a closer look.
 &lt;b&gt;Please do not be fanatic with limit 200&lt;/b&gt; - choose number that suites
 your project style. Limit 200 is empirical number base on some sources of at
 AT&amp;amp;T Bell Laboratories of 1988 year.
 &lt;/p&gt;</description>
         <properties>
            <property default-value="200" name="max" type="int">
               <description>Specify the maximum threshold allowed.</description>
            </property>
         </properties>
         <message-keys>
            <message-key key="npathComplexity"/>
         </message-keys>
      </check>
   </module>
</checkstyle-metadata>