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

Class ClassDataAbstractionCouplingCheck

java.lang.Object
com.puppycrawl.tools.checkstyle.api.AutomaticBean
com.puppycrawl.tools.checkstyle.api.AbstractViolationReporter
com.puppycrawl.tools.checkstyle.api.AbstractCheck
com.puppycrawl.tools.checkstyle.checks.metrics.AbstractClassCouplingCheck
com.puppycrawl.tools.checkstyle.checks.metrics.ClassDataAbstractionCouplingCheck
All Implemented Interfaces:
Configurable, Contextualizable
public final class ClassDataAbstractionCouplingCheck extends AbstractClassCouplingCheck

Measures the number of instantiations of other classes within the given class or record. This type of coupling is not caused by inheritance or the object oriented paradigm. Generally speaking, any data type with other data types as members or local variable that is an instantiation (object) of another class has data abstraction coupling (DAC). The higher the DAC, the more complex the structure of the class.

This check processes files in the following way:

  1. Iterates over the list of tokens (defined below) and counts all mentioned classes.
  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 7.
  • Property excludedClasses - Specify user-configured class names to ignore. Type is java.lang.String[]. Default value is ArrayIndexOutOfBoundsException, ArrayList, Boolean, Byte, Character, Class, Collection, Deprecated, Deque, Double, DoubleStream, EnumSet, Exception, Float, FunctionalInterface, HashMap, HashSet, IllegalArgumentException, IllegalStateException, IndexOutOfBoundsException, IntStream, Integer, LinkedHashMap, LinkedHashSet, LinkedList, List, Long, LongStream, Map, NullPointerException, Object, Optional, OptionalDouble, OptionalInt, OptionalLong, Override, Queue, RuntimeException, SafeVarargs, SecurityException, Set, Short, SortedMap, SortedSet, Stream, String, StringBuffer, StringBuilder, SuppressWarnings, Throwable, TreeMap, TreeSet, UnsupportedOperationException, Void, boolean, byte, char, double, float, int, long, short, var, void.
  • Property excludeClassesRegexps - Specify user-configured regular expressions to ignore classes. Type is java.util.regex.Pattern[]. Default value is ^$.
  • Property excludedPackages - Specify user-configured packages to ignore. Type is java.lang.String[]. Default value is "".

To configure the check: 

 <module name="ClassDataAbstractionCoupling"/>

Example:

The check passes without violations in the following: 

 class InputClassCoupling {
   Set set = new HashSet(); // HashSet ignored due to default excludedClasses property
   Map map = new HashMap(); // 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 InputClassCoupling {
   Set set = new HashSet(); // HashSet ignored due to default excludedClasses property
   Map map = new HashMap(); // HashMap ignored due to default excludedClasses property
   Date date = new Date(); // Counted, 1
   Time time = new Time(); // Counted, 2
   // instantiation of 5 other user defined classes
   Place place = new Place(); // violation, total is 8
 }

To configure the check with a threshold of 2: 

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

Example:

The check passes without violations in the following: 

 class InputClassCoupling {
   Set set = new HashSet(); // HashSet ignored due to default excludedClasses property
   Map map = new HashMap(); // 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 InputClassCoupling {
   Set set = new HashSet(); // HashSet ignored due to default excludedClasses property
   Map map = new HashMap(); // 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="ClassDataAbstractionCoupling">
   <property name="excludedClasses" value="HashMap, HashSet, Place"/>
 </module>

Example:

The check passes without violations in the following: 

 class InputClassCoupling {
   Set set = new HashSet(); // Ignored
   Map map = new HashMap(); // Ignored
   Date date = new Date(); // Counted, 1
   Time time = new Time(); // Counted, 2
   // instantiation of 5 other user defined classes
   Place place = new Place(); // Ignored
 }

The check results in a violation in the following: 

 class InputClassCoupling {
   Set set = new HashSet(); // Ignored
   Map map = new HashMap(); // Ignored
   Date date = new Date(); // Counted, 1
   Time time = new Time(); // Counted, 2
   // instantiation of 5 other user defined classes
   Space space = new Space(); // violation, total is 8
 }

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

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

Example:

The check passes without violations in the following: 

 class InputClassCoupling {
   Set set = new HashSet(); // HashSet ignored due to default excludedClasses property
   Map map = new HashMap(); // HashMap ignored due to default excludedClasses property
   Date date = new Date(); // Counted, 1
   Time time = new Time(); // Counted, 2
   // instantiation of 5 other user defined classes
   BufferedReader br = new BufferedReader(); // Ignored
 }

The check results in a violation in the following: 

 class InputClassCoupling {
   Set set = new HashSet(); // HashSet ignored due to default excludedClasses property
   Map map = new HashMap(); // HashMap ignored due to default excludedClasses property
   Date date = new Date(); // Counted, 1
   Time time = new Time(); // Counted, 2
   // instantiation of 5 other user defined classes
   File file = new File(); // violation, total is 8
 }

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

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

Example:

The check passes without violations in the following: 

 import java.io.BufferedReader;

 class InputClassCoupling {
   Set set = new HashSet(); // HashSet ignored due to default excludedClasses property
   Map map = new HashMap(); // HashMap ignored due to default excludedClasses property
   Date date = new Date(); // Counted, 1
   Time time = new Time(); // Counted, 2
   // instantiation of 5 other user defined classes
   BufferedReader br = new BufferedReader(); // Ignored
 }

The check results in a violation in the following: 

 import java.util.StringTokenizer;

 class InputClassCoupling {
   Set set = new HashSet(); // HashSet ignored due to default excludedClasses property
   Map map = new HashMap(); // HashMap ignored due to default excludedClasses property
   Date date = new Date(); // Counted, 1
   Time time = new Time(); // Counted, 2
   // instantiation of 5 other user defined classes
   StringTokenizer st = new StringTokenizer(); // violation, total is 8
 }

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="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;

 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:

  • classDataAbstractionCoupling
Since:
3.4

  • Field Details

    • MSG_KEY

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

    • DEFAULT_MAX

      private static final int DEFAULT_MAX
      Default allowed complexity.
      See Also:

  • Constructor Details

    • ClassDataAbstractionCouplingCheck

      public ClassDataAbstractionCouplingCheck()
      Creates bew instance of the check.

  • Method Details

    • 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:

    • 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:

    • getLogMessageId

      protected String getLogMessageId()
      Description copied from class: AbstractClassCouplingCheck
      Returns message key we use for log violations.
      Specified by:
      getLogMessageId in class AbstractClassCouplingCheck
      Returns:
      message key we use for log violations.