Content

BooleanExpressionComplexity

Since Checkstyle 3.4

Description

Restricts the number of boolean operators (&&, ||, &, | and ^) in an expression.

Rationale: Too many conditions leads to code that is difficult to read and hence debug and maintain.

Note that the operators & and | are not only integer bitwise operators, they are also the non-shortcut versions of the boolean operators && and ||.

Note that &, | and ^ are not checked if they are part of constructor or method call because they can be applied to non boolean variables and Checkstyle does not know types of methods from different classes.

Properties

name description type default value since
max Specify the maximum number of boolean operations allowed in one expression. int 3 3.4
tokens tokens to check subset of tokens LAND , BAND , LOR , BOR , BXOR . LAND , BAND , LOR , BOR , BXOR . 3.4

Examples

To configure the check:

<module name="BooleanExpressionComplexity"/>
        

Code Example:

public class Test
{
  public static void main(String ... args)
  {
    boolean a = true;
    boolean b = false;

    boolean c = (a & b) | (b ^ a);       // OK, 1(&) + 1(|) + 1(^) = 3 (max allowed 3)

    boolean d = (a & b) ^ (a || b) | a;  // violation, 1(&) + 1(^) + 1(||) + 1(|) = 4
  }
}
        

To configure the check with 5 allowed operation in boolean expression:

<module name="BooleanExpressionComplexity">
  <property name="max" value="5"/>
</module>
        

Code Example:

public class Test
{
  public static void main(String ... args)
  {
    boolean a = true;
    boolean b = false;

    boolean c = (a & b) | (b ^ a) | (a ^ b);   // OK, 1(&) + 1(|) + 1(^) + 1(|) + 1(^) = 5

    boolean d = (a | b) ^ (a | b) ^ (a || b) & b; // violation,
                                                 // 1(|) + 1(^) + 1(|) + 1(^) + 1(||) + 1(&) = 6
  }
}
        

To configure the check to ignore & and |:

<module name="BooleanExpressionComplexity">
  <property name="tokens" value="BXOR,LAND,LOR"/>
</module>
        

Code Example:

  public class Test
  {
    public static void main(String ... args)
    {
      boolean a = true;
      boolean b = false;

      boolean c = (!a && b) | (a || !b) ^ a;    // OK, 1(&&) + 1(||) + 1(^) = 3
                                                // | is ignored here

      boolean d = a ^ (a || b) ^ (b || a) & a; // violation, 1(^) + 1(||) + 1(^) + 1(||) = 4
                                               // & is ignored here
    }
  }
        

Example of Usage

Violation Messages

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

ClassDataAbstractionCoupling

Since Checkstyle 3.4

Description

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.

Properties

name description type default value since
max Specify the maximum threshold allowed. int 7 3.4
excludedClasses Specify user-configured class names to ignore. String[] 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, var, void 5.7
excludeClassesRegexps Specify user-configured regular expressions to ignore classes. Regular Expressions ^$ 7.7
excludedPackages Specify user-configured packages to ignore. String[] {} 7.7

Examples

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.

Example of Usage

Violation Messages

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

ClassFanOutComplexity

Since Checkstyle 3.4

Description

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.

Properties

name description type default value since
max Specify the maximum threshold allowed. int 20 3.4
excludedClasses Specify user-configured class names to ignore. String[] 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, var, void 5.7
excludeClassesRegexps Specify user-configured regular expressions to ignore classes. Regular Expressions ^$ 7.7
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. String[] {} 7.7

Examples

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
  int value = 10; // int is ignored due to default excludedClasses property
  void method() {
    var result = "result"; // var is ignored due to default excludedClasses property
  }
}
        

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.

Example of Usage

Violation Messages

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

CyclomaticComplexity

Since Checkstyle 3.2

Description

Checks cyclomatic complexity against a specified limit. It is a measure of the minimum number of possible paths through the source and therefore the number of required tests, it is not a about quality of code! It is only applied to methods, c-tors, static initializers and instance initializers.

The complexity is equal to the number of decision points + 1. Decision points: if, while , do, for, ?:, catch , switch, case statements and operators && and || in the body of target.

By pure theory level 1-4 is considered easy to test, 5-7 OK, 8-10 consider re-factoring to ease testing, and 11+ re-factor now as testing will be painful.

When it comes to code quality measurement by this metric level 10 is very good level as a ultimate target (that is hard to archive). Do not be ashamed to have complexity level 15 or even higher, but keep it below 20 to catch really bad designed code automatically.

Please use Suppression to avoid violations on cases that could not be split in few methods without damaging readability of code or encapsulation.

Properties

name description type default value since
max Specify the maximum threshold allowed. int 10 3.2
switchBlockAsSingleDecisionPoint Control whether to treat the whole switch block as a single decision point. boolean false 6.11
tokens tokens to check subset of tokens LITERAL_WHILE , LITERAL_DO , LITERAL_FOR , LITERAL_IF , LITERAL_SWITCH , LITERAL_CASE , LITERAL_CATCH , QUESTION , LAND , LOR . LITERAL_WHILE , LITERAL_DO , LITERAL_FOR , LITERAL_IF , LITERAL_SWITCH , LITERAL_CASE , LITERAL_CATCH , QUESTION , LAND , LOR . 3.2

Examples

To configure the check:

<module name="CyclomaticComplexity"/>
        

Example:

class CyclomaticComplexity {
  // Cyclomatic Complexity = 11
  int a, b, c, d, n;
  public void foo() { // 1, function declaration
    if (a == 1) { // 2, if
      fun1();
    } else if (a == b // 3, if
      && a == c) { // 4, && operator
      if (c == 2) { // 5, if
        fun2();
      }
    } else if (a == d) { // 6, if
      try {
        fun4();
      } catch (Exception e) { // 7, catch
      }
    } else {
      switch(n) {
        case 1: // 8, case
          fun1();
          break;
        case 2: // 9, case
          fun2();
          break;
        case 3: // 10, case
          fun3();
          break;
        default:
          break;
      }
    }
    d = a < 0 ? -1 : 1; // 11, ternary operator
  }
}
        

To configure the check with a threshold of 4 and check only for while and do-while loops:

<module name="CyclomaticComplexity">
  <property name="max" value="4"/>
  <property name="tokens" value="LITERAL_WHILE, LITERAL_DO"/>
</module>
        

Example:

class CyclomaticComplexity {
  // Cyclomatic Complexity = 5
  int a, b, c, d;
  public void foo() { // 1, function declaration
    while (a < b // 2, while
      && a > c) {
      fun();
    }
    if (a == b) {
      do { // 3, do
        fun();
      } while (d);
    } else if (c == d) {
      while (c > 0) { // 4, while
        fun();
      }
      do { // 5, do-while
        fun();
      } while (a);
    }
  }
}
        

To configure the check to consider switch-case block as one decision point.

<module name="CyclomaticComplexity">
  <property name="switchBlockAsSingleDecisionPoint" value="true"/>
</module>
        

Example:

class CyclomaticComplexity {
  // Cyclomatic Complexity = 11
  int a, b, c, d, e, n;
  public void foo() { // 1, function declaration
    if (a == b) { // 2, if
      fun1();
    } else if (a == 0 // 3, if
      && b == c) { // 4, && operator
      if (c == -1) { // 5, if
        fun2();
      }
    } else if (a == c // 6, if
      || a == d) { // 7, || operator
      fun3();
    } else if (d == e) { // 8, if
      try {
        fun4();
      } catch (Exception e) { // 9, catch
      }
    } else {
      switch(n) { // 10, switch
        case 1:
          fun1();
          break;
        case 2:
          fun2();
          break;
        default:
          break;
      }
    }
    a = a > 0 ? b : c; // 11, ternary operator
  }
}
        

Example of Usage

Violation Messages

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

JavaNCSS

Since Checkstyle 3.5

Description

Determines complexity of methods, classes and files by counting the Non Commenting Source Statements (NCSS). This check adheres to the specification for the JavaNCSS-Tool written by Chr. Clemens Lee.

Roughly said the NCSS metric is calculated by counting the source lines which are not comments, (nearly) equivalent to counting the semicolons and opening curly braces.

The NCSS for a class is summarized from the NCSS of all its methods, the NCSS of its nested classes and the number of member variable declarations.

The NCSS for a file is summarized from the ncss of all its top level classes, the number of imports and the package declaration.

Rationale: Too large methods and classes are hard to read and costly to maintain. A large NCSS number often means that a method or class has too many responsibilities and/or functionalities which should be decomposed into smaller units.

Properties

name description type default value since
methodMaximum Specify the maximum allowed number of non commenting lines in a method. int 50 3.5
classMaximum Specify the maximum allowed number of non commenting lines in a class. int 1500 3.5
fileMaximum Specify the maximum allowed number of non commenting lines in a file including all top level and nested classes. int 2000 3.5
recordMaximum Specify the maximum allowed number of non commenting lines in a record. int 150 8.36

Examples

To configure the check:

<module name="JavaNCSS"/>
        

Example:

public void test() {
  System.out.println("Line 1");
  // another 48 lines of code
  System.out.println("Line 50") // OK
  System.out.println("Line 51") // violation, the method crosses 50 non commented lines
}
        

To configure the check with 40 allowed non commented lines for a method:

<module name="JavaNCSS">
  <property name="methodMaximum" value="40"/>
</module>
        

Example:

public void test() {
  System.out.println("Line 1");
  // another 38 lines of code
  System.out.println("Line 40") // OK
  System.out.println("Line 41") // violation, the method crosses 40 non commented lines
}
        

To configure the check to set limit of non commented lines in class to 100:

<module name="JavaNCSS">
  <property name="classMaximum" value="100"/>
</module>
        

Example:

public class Test {
  public void test() {
    System.out.println("Line 1");
    // another 47 lines of code
    System.out.println("Line 49");
  }

  public void test1() {
    System.out.println("Line 50");  // OK
    // another 47 lines of code
    System.out.println("Line 98"); // violation
  }
}
        

To configure the check to set limit of non commented lines in file to 200:

<module name="JavaNCSS">
  <property name="fileMaximum" value="200"/>
</module>
        

Example:

public class Test1 {
  public void test() {
    System.out.println("Line 1");
    // another 48 lines of code
    System.out.println("Line 49");
  }

  public void test1() {
    System.out.println("Line 50");
    // another 47 lines of code
    System.out.println("Line 98"); // OK
  }
}

class Test2 {
  public void test() {
    System.out.println("Line 150"); // OK
  }

  public void test1() {
    System.out.println("Line 200"); // violation
  }
}
        

Example of Usage

Violation Messages

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

NPathComplexity

Since Checkstyle 3.4

Description

Checks the NPATH complexity against a specified limit.

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 && B, C || D, E ? F :G and their combinations).

The NPATH metric was designed base on Cyclomatic complexity to avoid problem of Cyclomatic complexity metric like nesting level within a function(method).

Metric was described at "NPATH: a measure of execution pathcomplexity and its applications". If you need detailed description of algorithm, please read that article, it is well written and have number of examples and details.

Here is some quotes:

An NPATH threshold value of 200 has been established for a function. The value 200 is based on studies done at AT&T Bell Laboratories [1988 year].
Some of the most effective methods of reducing the NPATH value include:
  • distributing functionality;
  • implementing multiple if statements as a switch statement;
  • creating a separate function for logical expressions with a high count of variables and (&&) and or (||) operators.
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.
Examples
Structure Complexity expression
if ([expr]) { [if-range] } NP(if-range) + 1 + NP(expr)
if ([expr]) { [if-range] } else { [else-range] } NP(if-range) + NP(else-range) + NP(expr)
while ([expr]) { [while-range] } NP(while-range) + NP(expr) + 1
do { [do-range] } while ([expr]) NP(do-range) + NP(expr) + 1
for([expr1]; [expr2]; [expr3]) { [for-range] } NP(for-range) + NP(expr1) + NP(expr2) + NP(expr3) + 1
switch ([expr]) { case : [case-range] default: [default-range] } S(i=1:i=n)NP(case-range[i]) + NP(default-range) + NP(expr)
[expr1] ? [expr2] : [expr3] NP(expr1) + NP(expr2) + NP(expr3) + 2
goto label 1
break 1
Expressions Number of && and || operators in expression. No operators - 0
continue 1
return 1
Statement (even sequential statements) 1
Empty block {} 1
Function call 1
Function(Method) declaration or Block P(i=1:i=N)NP(Statement[i])

Rationale: 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. Please do not be fanatic with limit 200 - choose number that suites your project style. Limit 200 is empirical number base on some sources of at AT&T Bell Laboratories of 1988 year.

Properties

name description type default value since
max Specify the maximum threshold allowed. int 200 3.4

Examples

To configure the check:

<module name="NPathComplexity"/>
        

Example:

public abstract class Test {

final int a = 0;
int b = 0;

public void foo() { // OK, NPath complexity is less than default threshold
  // function consists of one if-else block with an NPath Complexity of 3
  if (a > 10) {
    if (a > b) { // nested if-else decision tree adds 2 to the complexity count
      buzz();
    } else {
      fizz();
    }
  } else { // last possible outcome of the main if-else block, adds 1 to complexity
    buzz();
  }
}

public void boo() { // violation, NPath complexity is 217 (max allowed is 200)
  // looping through 3 switch statements produces 6^3 + 1 (217) possible outcomes
  for(int i = 0; i < b; i++) { // for statement adds 1 to final complexity
    switch(i) { // each independent switch statement multiplies complexity by 6
      case a:
        // ternary with && adds 3 to switch's complexity
        print(f(i) && g(i) ? fizz() : buzz());
      default:
        // ternary with || adds 3 to switch's complexity
        print(f(i) || g(i) ? fizz() : buzz());
    }
    switch(i - 1) { // multiplies complexity by 6
      case a:
        print(f(i) && g(i) ? fizz() : buzz());
      default:
        print(f(i) || g(i) ? fizz() : buzz());
    }
    switch(i + 1) { // multiplies complexity by 6
      case a:
        print(f(i) && g(i) ? fizz() : buzz());
      default:
        print(f(i) || g(i) ? fizz() : buzz());
    }
  }
}

public abstract boolean f(int x);
public abstract boolean g(int x);
public abstract String fizz();
public abstract String buzz();
public abstract void print(String str);
}
        

To configure the check with a threshold of 100:

<module name="NPathComplexity">
  <property name="max" value="100"/>
</module>
        

Example:

public abstract class Test1 {
public void foo() { // violation, NPath complexity is 128 (max allowed is 100)
  int a,b,t,m,n;
  a=b=t=m=n = 0;

  // Complexity is achieved by choosing from 2 options 7 times (2^7 = 128 possible outcomes)
  if (a > b) { // non-nested if-else decision tree multiplies complexity by 2
    bar();
  } else {
    baz();
  }

  print(t > 1 ? bar() : baz()); // 5 ternary statements multiply complexity by 2^5
  print(t > 2 ? bar() : baz());
  print(t > 3 ? bar() : baz());
  print(t > 4 ? bar() : baz());
  print(t > 5 ? bar() : baz());

  if (m > n) { // multiplies complexity by 2
    baz();
  } else {
    bar();
  }
}

public abstract String bar();
public abstract String baz();
public abstract void print(String str);
}
        

Example of Usage

Violation Messages

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