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

Class JavaNCSSCheck

java.lang.Object
com.puppycrawl.tools.checkstyle.AbstractAutomaticBean
com.puppycrawl.tools.checkstyle.api.AbstractViolationReporter
com.puppycrawl.tools.checkstyle.api.AbstractCheck
com.puppycrawl.tools.checkstyle.checks.metrics.JavaNCSSCheck
All Implemented Interfaces:
Configurable, Contextualizable
public class JavaNCSSCheck extends AbstractCheck
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.

Here is a breakdown of what exactly is counted and not counted:

JavaNCSS metrics
StructureNCSS CountNotes
Package declaration1 Counted at the terminating semicolon.
Import declaration1 Each single, static, or wildcard import counts as 1.
Class, Interface, Annotation (@interface)1 Counted at the opening curly brace of the body.
Method, Constructor1 Counted at the declaration.
Static initializer, Instance initializer1 Both static {} and bare {} initializer blocks count as 1.
Annotation type member1 Each method-like member declaration inside @interface counts as 1. A standalone ; inside @interface also counts as 1.
Variable declaration1 1 per statement regardless of how many variables are declared on that line. int x, y; counts as 1.
if1 The if keyword counts as 1.
else, else if1 The else keyword counts as 1, separate from the if count.
while, do, for1 The keyword header counts as 1.
switch1 The switch keyword counts as 1.
case, default1 Every case and default label adds 1.
try0 The try keyword itself does not count.
catch1 Each catch block counts as 1.
finally1 The finally block counts as 1.
synchronized1 The synchronized statement counts as 1.
return, break, continue, throw1 Each counts as 1.
assert1 Each assert statement counts as 1, with or without a message expression.
Labeled statement1 label: statement counts as 1.
Explicit constructor invocation1 this() or super() calls inside a constructor body each count as 1.
Expression statements (assignments, method calls)1 Statement-level expressions terminated by ; count as 1. A method call inside a return does not add an extra count.
Empty blocks {}0 Empty curly braces do not increase the count.
Empty statements ;0 Standalone semicolons outside of @interface do not increase the count.
Since:
3.5

  • Field Details

  • Constructor Details

  • Method Details

    • getDefaultTokens

      public int[] getDefaultTokens()
      Description copied from class: AbstractCheck
      Returns the default token a check is interested in. Only used if the configuration for a check does not define the tokens.
      Specified by:
      getDefaultTokens in class AbstractCheck
      Returns:
      the default tokens
      See Also:

    • 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:

    • beginTree

      public void beginTree(DetailAST rootAST)
      Description copied from class: AbstractCheck
      Called before the starting to process a tree. Ideal place to initialize information that is to be collected whilst processing a tree.
      Overrides:
      beginTree in class AbstractCheck
      Parameters:
      rootAST - the root of the tree

    • visitToken

      public void visitToken(DetailAST ast)
      Description copied from class: AbstractCheck
      Called to process a token.
      Overrides:
      visitToken in class AbstractCheck
      Parameters:
      ast - the token to process

    • leaveToken

      public void leaveToken(DetailAST ast)
      Description copied from class: AbstractCheck
      Called after all the child nodes have been process.
      Overrides:
      leaveToken in class AbstractCheck
      Parameters:
      ast - the token leaving

    • finishTree

      public void finishTree(DetailAST rootAST)
      Description copied from class: AbstractCheck
      Called after finished processing a tree. Ideal place to report on information collected whilst processing a tree.
      Overrides:
      finishTree in class AbstractCheck
      Parameters:
      rootAST - the root of the tree

    • setFileMaximum

      public void setFileMaximum(int fileMaximum)
      Setter to specify the maximum allowed number of non commenting lines in a file including all top level and nested classes.
      Parameters:
      fileMaximum - the maximum ncss
      Since:
      3.5

    • setClassMaximum

      public void setClassMaximum(int classMaximum)
      Setter to specify the maximum allowed number of non commenting lines in a class.
      Parameters:
      classMaximum - the maximum ncss
      Since:
      3.5

    • setRecordMaximum

      public void setRecordMaximum(int recordMaximum)
      Setter to specify the maximum allowed number of non commenting lines in a record.
      Parameters:
      recordMaximum - the maximum ncss
      Since:
      8.36

    • setMethodMaximum

      public void setMethodMaximum(int methodMaximum)
      Setter to specify the maximum allowed number of non commenting lines in a method.
      Parameters:
      methodMaximum - the maximum ncss
      Since:
      3.5

    • isCountable

      private static boolean isCountable(DetailAST ast)
      Checks if a token is countable for the ncss metric.
      Parameters:
      ast - the AST
      Returns:
      true if the token is countable

    • isVariableDefCountable

      private static boolean isVariableDefCountable(DetailAST ast)
      Checks if a variable definition is countable.
      Parameters:
      ast - the AST
      Returns:
      true if the variable definition is countable, false otherwise

    • isExpressionCountable

      private static boolean isExpressionCountable(DetailAST ast)
      Checks if an expression is countable for the ncss metric.
      Parameters:
      ast - the AST
      Returns:
      true if the expression is countable, false otherwise

    • isMethodOrCtorOrInitDefinition

      private static boolean isMethodOrCtorOrInitDefinition(int tokenType)
      Checks if a token is a method, constructor, or compact constructor definition.
      Parameters:
      tokenType - the type of token we are checking
      Returns:
      true if token type is method or ctor definition, false otherwise