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.

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

JavaNCSS metrics
Structure	NCSS Count	Notes
Package declaration	1	Counted at the terminating semicolon.
Import declaration	1	Each single, static, or wildcard import counts as 1.
Class, Interface, Annotation (`@interface`)	1	Counted at the opening curly brace of the body.
Method, Constructor	1	Counted at the declaration.
Static initializer, Instance initializer	1	Both `static {}` and bare `{}` initializer blocks count as 1.
Annotation type member	1	Each method-like member declaration inside `@interface` counts as 1. A standalone `;` inside `@interface` also counts as 1.
Variable declaration	1	1 per statement regardless of how many variables are declared on that line. `int x, y;` counts as 1.
`if`	1	The `if` keyword counts as 1.
`else`, `else if`	1	The `else` keyword counts as 1, separate from the `if` count.
`while`, `do`, `for`	1	The keyword header counts as 1.
`switch`	1	The `switch` keyword counts as 1.
`case`, `default`	1	Every case and default label adds 1.
`try`	0	The `try` keyword itself does not count.
`catch`	1	Each catch block counts as 1.
`finally`	1	The finally block counts as 1.
`synchronized`	1	The synchronized statement counts as 1.
`return`, `break`, `continue`, `throw`	1	Each counts as 1.
`assert`	1	Each assert statement counts as 1, with or without a message expression.
Labeled statement	1	`label: statement` counts as 1.
Explicit constructor invocation	1	`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.

Properties

name	description	type	default value	since
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
methodMaximum	Specify the maximum allowed number of non commenting lines in a method.	int	`50`	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="Checker">
  <module name="TreeWalker">
    <module name="JavaNCSS"/>
  </module>
</module>

Example1:


package com.puppycrawl.tools.checkstyle.checks.metrics.javancss;

class Example1 {

  public void testMethod1() {
    System.out.println("m-1:Line 1");
    System.out.println("m-1:Line 2");
    System.out.println("m-1:Line 3");
    System.out.println("m-1:Line 4");
    System.out.println("m-1:Line 5");
  }

  public void testMethod2() {
    System.out.println("m-2:Line 1");
    System.out.println("m-2:Line 2");
    System.out.println("m-2:Line 3");
  }
}

To configure the check with 4 allowed non commented lines for a method:


<module name="Checker">
  <module name="TreeWalker">
    <module name="JavaNCSS">
      <property name="methodMaximum" value="4"/>
    </module>
  </module>
</module>

Example2:


package com.puppycrawl.tools.checkstyle.checks.metrics.javancss;

class Example2 {
  // violation below, 'NCSS for this method is 6 (max allowed is 4)'
  public void testMethod1() {
    System.out.println("m-1:Line 1");
    System.out.println("m-1:Line 2");
    System.out.println("m-1:Line 3");
    System.out.println("m-1:Line 4");
    System.out.println("m-1:Line 5");
  }

  public void testMethod2() {
    System.out.println("m-2:Line 1");
    System.out.println("m-2:Line 2");
    System.out.println("m-2:Line 3");
  }
}

To configure the check to set limit of non commented lines in class to 10:


<module name="Checker">
  <module name="TreeWalker">
    <module name="JavaNCSS">
      <property name="classMaximum" value="10"/>
    </module>
  </module>
</module>

Example3:


package com.puppycrawl.tools.checkstyle.checks.metrics.javancss;

class Example3 {
  // violation above, 'NCSS for this class is 11 (max allowed is 10)'
  public void testMethod1() {
    System.out.println("m-1:Line 1");
    System.out.println("m-1:Line 2");
    System.out.println("m-1:Line 3");
    System.out.println("m-1:Line 4");
    System.out.println("m-1:Line 5");
  }

  public void testMethod2() {
    System.out.println("m-2:Line 1");
    System.out.println("m-2:Line 2");
    System.out.println("m-2:Line 3");
  }
}

To configure the check to set limit of non commented lines in file to 10:


<module name="Checker">
  <module name="TreeWalker">
    <module name="JavaNCSS">
      <property name="fileMaximum" value="10"/>
    </module>
  </module>
</module>

Example4:


package com.puppycrawl.tools.checkstyle.checks.metrics.javancss;
// violation above, 'NCSS for this file is 12 (max allowed is 10)'
class Example4 {

  public void testMethod1() {
    System.out.println("m-1:Line 1");
    System.out.println("m-1:Line 2");
    System.out.println("m-1:Line 3");
    System.out.println("m-1:Line 4");
    System.out.println("m-1:Line 5");
  }

  public void testMethod2() {
    System.out.println("m-2:Line 1");
    System.out.println("m-2:Line 2");
    System.out.println("m-2:Line 3");
  }
}

To configure the check to set limit of non commented lines in record to 5:


<module name="Checker">
  <module name="TreeWalker">
    <module name="JavaNCSS">
      <property name="recordMaximum" value="5"/>
    </module>
  </module>
</module>

Example5:


package com.puppycrawl.tools.checkstyle.checks.metrics.javancss;

public class Example5 {
  // This record has NCSS = 5, which is OK
  record ValidRecord(int a, int b) {
    public ValidRecord {
      System.out.println("Line 1");
      System.out.println("Line 2");
      System.out.println("Line 3");
    }
  }

  // violation below, 'NCSS for this record is 6 (max allowed is 5)'
  record InvalidRecord(int x, int y) {
    public InvalidRecord {
      System.out.println("Line 1");
      System.out.println("Line 2");
      System.out.println("Line 3");
      System.out.println("Line 4");
    }
  }
}

Example of Usage

Checkstyle Style

Violation Messages

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

Fully Qualified Name

com.puppycrawl.tools.checkstyle.checks.metrics.JavaNCSSCheck

Use this fully qualified class name in configuration when an exact class reference is required.

Parent Module

TreeWalker