Package com.puppycrawl.tools.checkstyle.checks.metrics

Class ClassFanOutComplexityCheck

  • All Implemented Interfaces:
    Configurable, Contextualizable
    public final class ClassFanOutComplexityCheck
extends AbstractClassCouplingCheck

    Checks the number of other types a given class/record/interface/enum/annotation relies on. Also the square of this has been shown to indicate the amount of maintenance required in functional programs (on a file basis) at least.

    This check processes files in the following way:

    1. Iterates over all tokens that might contain type reference.
    2. If a class was imported with direct import (i.e. import java.math.BigDecimal), or the class was referenced with the package name (i.e. java.math.BigDecimal value) and the package was added to the excludedPackages parameter, the class does not increase complexity.
    3. If a class name was added to the excludedClasses parameter, the class does not increase complexity.
    • Property max - Specify the maximum threshold allowed. Type is int. Default value is 20.
    • Property excludedClasses - Specify user-configured class names to ignore. Type is java.lang.String[]. Default value is ArrayIndexOutOfBoundsException, ArrayList, Boolean, Byte, Character, Class, Deprecated, Deque, Double, Exception, Float, FunctionalInterface, HashMap, HashSet, IllegalArgumentException, IllegalStateException, IndexOutOfBoundsException, Integer, LinkedList, List, Long, Map, NullPointerException, Object, Override, Queue, RuntimeException, SafeVarargs, SecurityException, Set, Short, SortedMap, SortedSet, String, StringBuffer, StringBuilder, SuppressWarnings, Throwable, TreeMap, TreeSet, UnsupportedOperationException, Void, boolean, byte, char, double, float, int, long, short, void.
    • Property excludeClassesRegexps - Specify user-configured regular expressions to ignore classes. Type is java.lang.String[]. Validation type is java.util.regex.Pattern. Default value is ^$.
    • Property excludedPackages - Specify user-configured packages to ignore. All excluded packages should end with a period, so it also appends a dot to a package name. Type is java.lang.String[]. Default value is "".

    To configure the check: 

     <module name="ClassFanOutComplexity"/>

    Example:

    The check passes without violations in the following: 

     class InputClassComplexity {
   Set set = new HashSet(); // Set, HashSet ignored due to default excludedClasses property
   Map map = new HashMap(); // Map, HashMap ignored due to default excludedClasses property
   Date date = new Date(); // Counted, 1
   Time time = new Time(); // Counted, 2
   Place place = new Place(); // Counted, 3
 }

    The check results in a violation in the following: 

     class InputClassComplexity {
   Set set = new HashSet(); // Set, HashSet ignored due to default excludedClasses property
   Map map = new HashMap(); // Map, HashMap ignored due to default excludedClasses property
   Date date = new Date(); // Counted, 1
   Time time = new Time(); // Counted, 2
   // mention of 18 other user defined classes
   Place place = new Place(); // violation, total is 21
 }

    To configure the check with a threshold of 2: 

     <module name="ClassFanOutComplexity">
   <property name="max" value="2"/>
 </module>

    Example:

    The check passes without violations in the following: 

     class InputClassComplexity {
   Set set = new HashSet(); // Set, HashSet ignored due to default excludedClasses property
   Map map = new HashMap(); // Map, HashMap ignored due to default excludedClasses property
   Date date = new Date(); // Counted, 1
   Time time = new Time(); // Counted, 2
 }

    The check results in a violation in the following: 

     class InputClassComplexity {
   Set set = new HashSet(); // Set, HashSet ignored due to default excludedClasses property
   Map map = new HashMap(); // Map, HashMap ignored due to default excludedClasses property
   Date date = new Date(); // Counted, 1
   Time time = new Time(); // Counted, 2
   Place place = new Place(); // violation, total is 3
 }

    To configure the check with three excluded classes HashMap, HashSet and Place: 

     <module name="ClassFanOutComplexity">
   <property name="excludedClasses" value="HashMap, HashSet, Place"/>
 </module>

    Example:

    The check passes without violations in the following: 

     class InputClassComplexity {
   Set set = new HashSet(); // Set counted 1, HashSet ignored
   Map map = new HashMap(); // Map counted 2, HashMap ignored
   Date date = new Date(); // Counted, 3
   Time time = new Time(); // Counted, 4
   // mention of 16 other user defined classes
   Place place = new Place(); // Ignored
 }

    The check results in a violation in the following: 

     class InputClassComplexity {
   Set set = new HashSet(); // Set counted 1, HashSet ignored
   Map map = new HashMap(); // Map counted 2, HashMap ignored
   Date date = new Date(); // Counted, 3
   Time time = new Time(); // Counted, 4
   // mention of 16 other user defined classes
   Space space = new Space(); // violation, total is 21
 }

    To configure the check to exclude classes with a regular expression .*Reader$: 

     <module name="ClassFanOutComplexity">
   <property name="excludeClassesRegexps" value=".*Reader$"/>
 </module>

    Example:

    The check passes without violations in the following: 

     class InputClassComplexity {
   Set set = new HashSet(); // Set, HashSet ignored due to default excludedClasses property
   Map map = new HashMap(); // Map, HashMap ignored due to default excludedClasses property
   Date date = new Date(); // Counted, 1
   Time time = new Time(); // Counted, 2
   // mention of 18 other user defined classes
   BufferedReader br; // Ignored
 }

    The check results in a violation in the following: 

     class InputClassComplexity {
   Set set = new HashSet(); // Set, HashSet ignored due to default excludedClasses property
   Map map = new HashMap(); // Map, HashMap ignored due to default excludedClasses property
   Date date = new Date(); // Counted, 1
   Time time = new Time(); // Counted, 2
   // mention of 18 other user defined classes
   File file; // violation, total is 21
 }

    To configure the check with an excluded package java.io: 

     <module name="ClassFanOutComplexity">
   <property name="excludedPackages" value="java.io"/>
 </module>

    Example:

    The check passes without violations in the following: 

     import java.io.BufferedReader;

 class InputClassComplexity {
   Set set = new HashSet(); // Set, HashSet ignored due to default excludedClasses property
   Map map = new HashMap(); // Map, HashMap ignored due to default excludedClasses property
   Date date = new Date(); // Counted, 1
   Time time = new Time(); // Counted, 2
   // mention of 18 other user defined classes
   BufferedReader br; // Ignored
 }

    The check results in a violation in the following: 

     import java.util.StringTokenizer;

 class InputClassComplexity {
   Set set = new HashSet(); // Set, HashSet ignored due to default excludedClasses property
   Map map = new HashMap(); // Map, HashMap ignored due to default excludedClasses property
   Date date = new Date(); // Counted, 1
   Time time = new Time(); // Counted, 2
   // mention of 18 other user defined classes
   StringTokenizer st; // violation, total is 21
 }

    Override property excludedPackages to mark some packages as excluded. Each member of excludedPackages should be a valid identifier:

    • java.util - valid, excludes all classes inside java.util, but not from the subpackages.
    • java.util. - invalid, should not end with a dot.
    • java.util.* - invalid, should not end with a star.

    Note, that checkstyle will ignore all classes from the java.lang package and its subpackages, even if the java.lang was not listed in the excludedPackages parameter.

    Also note, that excludedPackages will not exclude classes, imported via wildcard (e.g. import java.math.*). Instead of wildcard import you should use direct import (e.g. import java.math.BigDecimal).

    Also note, that checkstyle will not exclude classes within the same file even if it was listed in the excludedPackages parameter. For example, assuming the config is 

     <module name="ClassFanOutComplexity">
   <property name="excludedPackages" value="a.b"/>
 </module>

    And the file a.b.Foo.java is: 

     package a.b;

 import a.b.Bar;
 import a.b.c.Baz;

 class Foo {
   Bar bar; // Will be ignored, located inside ignored a.b package
   Baz baz; // Will not be ignored, located inside a.b.c package
   Data data; // Will not be ignored, same file

   class Data {
     Foo foo; // Will not be ignored, same file
   }
 }

    The bar member will not be counted, since the a.b added to the excludedPackages. The baz member will be counted, since the a.b.c was not added to the excludedPackages. The data and foo members will be counted, as they are inside same file.

    Parent is com.puppycrawl.tools.checkstyle.TreeWalker

    Violation Message Keys:

    • classFanOutComplexity
    Since:
    3.4

    • Field Detail

      • MSG_KEY

        public static final java.lang.String MSG_KEY
        A key is pointing to the warning message text in "messages.properties" file.
        See Also:
        Constant Field Values

    • Constructor Detail

      • ClassFanOutComplexityCheck

        public ClassFanOutComplexityCheck()
        Creates new instance of this check.

    • Method Detail

      • getRequiredTokens

        public int[] getRequiredTokens()
        Description copied from class: AbstractCheck
        The tokens that this check must be registered for.
        Specified by:
        getRequiredTokens in class AbstractCheck
        Returns:
        the token set this must be registered for.
        See Also:
        TokenTypes

      • getAcceptableTokens

        public int[] getAcceptableTokens()
        Description copied from class: AbstractCheck
        The configurable token set. Used to protect Checks against malicious users who specify an unacceptable token set in the configuration file. The default implementation returns the check's default tokens.
        Specified by:
        getAcceptableTokens in class AbstractCheck
        Returns:
        the token set this check is designed for.
        See Also:
        TokenTypes