Class ClassFanOutComplexityCheck

  • All Implemented Interfaces:
    Configurable, Contextualizable

    public final class ClassFanOutComplexityCheck
    extends AbstractClassCouplingCheck

    Checks the number of other classes a given class 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. Default value is 20.
    • Property excludedClasses - Specify user-configured class names to ignore. 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. 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. Default value is {}.

    To configure the check:

     <module name="ClassFanOutComplexity"/>
     

    To configure the check with a threshold of 10:

     <module name="ClassFanOutComplexity">
       <property name="max" value="10"/>
     </module>
     

    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 node, 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="ClassDataAbstractionCoupling">
       <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;
    
     public class Foo {
       public Bar bar; // Will be ignored, located inside ignored a.b package
       public Baz baz; // Will not be ignored, located inside a.b.c package
       public Data data; // Will not be ignored, same file
    
       class Data {
         public 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.

    Example of usage:

     <module name="ClassFanOutComplexity">
       <property name="excludedPackages" value="java.util, java.math"/>
     </module>
     
    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