Description

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.

Properties

Examples

To configure the check:

<module name="Checker">
  <module name="TreeWalker">
    <module name="ClassFanOutComplexity"/>
  </module>
</module>
        

Example1:

The check passes without violations in the following:

class Example1{
  Set set = new HashSet(); // Set, HashSet ignored
  Map map = new HashMap(); // Map, HashMap ignored
  Date date = new Date(); // Counted, 1
  Time1 time = new Time1(); // Counted, 2
  Place1 place = new Place1(); // Counted, 3
  int value = 10; // int is ignored
  BufferedReader br;
  File file;
  void method() {
    var result = "result"; // var is ignored
  }
}
class Place1 {}
class Time1 {}
        

To configure the check with a threshold of 2:

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

Example2:

The check results in a violation in the following:

class Example2{ // violation 'Class Fan-Out Complexity is 5 (max allowed is 2)'
  Set set = new HashSet(); // Set, HashSet ignored
  Map map = new HashMap(); // Map, HashMap ignored
  Date date = new Date(); // Counted, 1
  Time2 time = new Time2(); // Counted, 2
  Place2 place = new Place2(); // Counted, 3
  int value = 10; // int is ignored
  BufferedReader br; // Counted, 4
  File file; // Counted, 5
  void method() {
    var result = "result"; // var is ignored
  }
}
class Place2 {}
class Time2 {}
        

To configure the check with three excluded classes HashMap, HashSet and Place3:

<module name="Checker">
  <module name="TreeWalker">
    <module name="ClassFanOutComplexity">
      <property name="excludedClasses" value="HashMap, HashSet, Place3"/>
      <property name="max" value="3"/>
    </module>
  </module>
</module>
        

Example3:

The check results in a violation in the following:

class Example3{ // violation 'Class Fan-Out Complexity is 7 (max allowed is 3)'
  Set set = new HashSet(); // Set counted 1, HashSet ignored
  Map map = new HashMap(); // Map counted 2, HashMap ignored
  Date date = new Date(); // Counted, 3
  Time3 time = new Time3(); // Counted, 4
  Place3 place = new Place3(); // Counted, 5
  int value = 10; // int is ignored
  BufferedReader br; // Counted, 6
  File file; // Counted, 7
  void method() {
    var result = "result"; // var is ignored
  }
}
class Place3 {}
class Time3 {}
        

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

<module name="Checker">
  <module name="TreeWalker">
    <module name="ClassFanOutComplexity">
      <property name="excludeClassesRegexps" value=".*Reader$"/>
      <property name="max" value="3"/>
    </module>
  </module>
</module>
        

Example4:

The check results in a violation in the following:

class Example4{ // violation 'Class Fan-Out Complexity is 4 (max allowed is 3)'
  Set set = new HashSet(); // Set, HashSet ignored
  Map map = new HashMap(); // Map, HashMap ignored
  Date date = new Date(); // Counted, 1
  Time4 time = new Time4(); // Counted, 2
  Place4 place = new Place4(); // Counted, 3
  int value = 10; // int is ignored
  BufferedReader br; // Ignored
  File file; // Counted, 4
  void method() {
    var result = "result"; // var is ignored
  }
}
class Place4 {}
class Time4 {}
        

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

<module name="Checker">
  <module name="TreeWalker">
    <module name="ClassFanOutComplexity">
      <property name="excludedPackages" value="java.io"/>
      <property name="max" value="5"/>
    </module>
  </module>
</module>
        

Example5:

The check passes without violations in the following:

class Example5{
  Set set = new HashSet(); // Set, HashSet ignored
  Map map = new HashMap(); // Map, HashMap ignored
  Date date = new Date(); // Counted, 1
  Time5 time = new Time5(); // Counted, 2
  Place5 place = new Place5(); // Counted, 3
  int value = 10; // int is ignored
  BufferedReader br; // Ignored
  File file; // Ignored
  void method() {
    var result = "result"; // var is ignored
  }
}
class Place5 {}
class Time5 {}
        

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="Checker">
  <module name="TreeWalker">
    <module name="ClassFanOutComplexity">
      <property name="excludedPackages" value="java.util"/>
      <property name="max" value="3"/>
    </module>
  </module>
</module>
        

Example6:

And the file is:

class Example6{ // violation 'Class Fan-Out Complexity is 4 (max allowed is 3)'
  Set set = new HashSet(); // Set, HashSet ignored
  Map map = new HashMap(); // Map, HashMap ignored
  Date date = new Date(); // Ignored
  Time6 time = new Time6(); // Counted, 1
  Place6 place = new Place6(); // Counted, 2
  int value = 10; // int is ignored
  BufferedReader br; // Counted, 3
  File file; // Counted, 4
  void method() {
    var result = "result"; // var is ignored
  }
}
class Place6 {}
class Time6 {}
        

The Set, Map, HashMap, HashSet, Date member will not be counted, since the java.util added to the excludedPackages. The BufferReader, File member will be counted,

Example of Usage

• Checkstyle Style

Violation Messages

• classFanOutComplexity

All messages can be customized if the default message doesn't suit you. Please see the documentation to learn how to.

Package

com.puppycrawl.tools.checkstyle.checks.metrics

Parent Module

TreeWalker