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
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");
  }
}

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