com.puppycrawl.tools.checkstyle.checks

Class TrailingCommentCheck

java.lang.Object

com.puppycrawl.tools.checkstyle.api.AutomaticBean

com.puppycrawl.tools.checkstyle.api.AbstractViolationReporter

com.puppycrawl.tools.checkstyle.api.Check

com.puppycrawl.tools.checkstyle.checks.AbstractFormatCheck

com.puppycrawl.tools.checkstyle.checks.TrailingCommentCheck

All Implemented Interfaces:

Configurable, Contextualizable

public class TrailingCommentCheck
extends AbstractFormatCheck

The check to ensure that requires that comments be the only thing on a line. For the case of // comments that means that the only thing that should precede it is whitespace. It doesn't check comments if they do not end line, i.e. it accept the following: Thread.sleep( 10 <some comment here> ); Format property is intended to deal with the "} // while" example.

Rationale: Steve McConnel in "Code Complete" suggests that endline comments are a bad practice. An end line comment would be one that is on the same line as actual code. For example:

  a = b + c;      // Some insightful comment
  d = e / f;        // Another comment for this line
 

Quoting "Code Complete" for the justification:

• "The comments have to be aligned so that they do not interfere with the visual structure of the code. If you don't align them neatly, they'll make your listing look like it's been through a washing machine."
• "Endline comments tend to be hard to format...It takes time to align them. Such time is not spent learning more about the code; it's dedicated solely to the tedious task of pressing the spacebar or tab key."
• "Endline comments are also hard to maintain. If the code on any line containing an endline comment grows, it bumps the comment farther out, and all the other endline comments will have to bumped out to match. Styles that are hard to maintain aren't maintained...."
• "Endline comments also tend to be cryptic. The right side of the line doesn't offer much room and the desire to keep the comment on one line means the comment must be short. Work then goes into making the line as short as possible instead of as clear as possible. The comment usually ends up as cryptic as possible...."
• "A systemic problem with endline comments is that it's hard to write a meaningful comment for one line of code. Most endline comments just repeat the line of code, which hurts more than it helps."

His comments on being hard to maintain when the size of the line changes are even more important in the age of automated refactorings.

To configure the check so it enforces only comment on a line:

 <module name="TrailingComment">
    <property name="format" value="^\\s*$"/>
 </module>
 

Author:

o_sukhodolsky

Constructor Summary

Constructors

Constructor and Description
TrailingCommentCheck() Creates new instance of the check.

Method Summary

Methods

Modifier and Type	Method and Description
void	beginTree(DetailAST rootAST) Called before the starting to process a tree.
int[]	getDefaultTokens() Returns the default token a check is interested in.
void	setLegalComment(String format) Sets patter for legal trailing comments.
void	visitToken(DetailAST ast) Called to process a token.

Methods inherited from class com.puppycrawl.tools.checkstyle.checks.AbstractFormatCheck

getFormat, getRegexp, setCompileFlags, setFormat

Methods inherited from class com.puppycrawl.tools.checkstyle.api.Check

destroy, finishTree, getAcceptableTokens, getClassLoader, getFileContents, getLine, getLines, getRequiredTokens, getTabWidth, getTokenNames, init, isCommentNodesRequired, leaveToken, log, log, setClassLoader, setFileContents, setMessages, setTabWidth, setTokens

Methods inherited from class com.puppycrawl.tools.checkstyle.api.AbstractViolationReporter

getCustomMessages, getId, getMessageBundle, getSeverity, getSeverityLevel, log, setId, setSeverity

Methods inherited from class com.puppycrawl.tools.checkstyle.api.AutomaticBean

configure, contextualize, finishLocalSetup, getConfiguration, setupChild

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

TrailingCommentCheck

public TrailingCommentCheck()
                     throws org.apache.commons.beanutils.ConversionException

Creates new instance of the check.

Throws:

org.apache.commons.beanutils.ConversionException - unable to parse DEFAULT_FORMAT.

Method Detail

setLegalComment

public void setLegalComment(String format)
                     throws org.apache.commons.beanutils.ConversionException

Sets patter for legal trailing comments.

Parameters:

format - format to set.

Throws:

org.apache.commons.beanutils.ConversionException - unable to parse a given format.

getDefaultTokens

public int[] getDefaultTokens()

Description copied from class: Check

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 Check

Returns:

the default tokens

See Also:

TokenTypes

visitToken

public void visitToken(DetailAST ast)

Description copied from class: Check

Called to process a token.

Overrides:

visitToken in class Check

Parameters:

ast - the token to process

beginTree

public void beginTree(DetailAST rootAST)

Description copied from class: Check

Called before the starting to process a tree. Ideal place to initialise information that is to be collected whilst processing a tree.

Overrides:

beginTree in class Check

Parameters:

rootAST - the root of the tree