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.AbstractCheck

com.puppycrawl.tools.checkstyle.checks.TrailingCommentCheck

All Implemented Interfaces:

Configurable, Contextualizable

public class TrailingCommentCheck
extends AbstractCheck

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 a line; for example, it accepts the following: Thread.sleep( 10 /*some comment here*/ ); Format property is intended to deal with the } // while example.

Rationale: Steve McConnell 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."

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

• Property format - Specify pattern for strings allowed before the comment. Type is java.util.regex.Pattern. Default value is "^[\s});]*$".
• Property legalComment - Define pattern for text allowed in trailing comments. (This pattern will not be applied to multiline comments and the text of the comment will be trimmed before matching.) Type is java.util.regex.Pattern. Default value is null.

To configure the check:

 <module name="TrailingComment"/>
 

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

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

Parent is com.puppycrawl.tools.checkstyle.TreeWalker

Violation Message Keys:

• trailing.comments

Since:

3.4

Nested Class Summary

Nested classes/interfaces inherited from class com.puppycrawl.tools.checkstyle.api.AutomaticBean

AutomaticBean.OutputStreamOptions

Field Summary

Fields

Modifier and Type	Field and Description
static String	MSG_KEY A key is pointing to the warning message text in "messages.properties" file.

Constructor Summary

Constructors

Constructor and Description
TrailingCommentCheck()

Method Summary

Modifier and Type	Method and Description
void	beginTree(DetailAST rootAST) Called before the starting to process a tree.
int[]	getAcceptableTokens() The configurable token set.
int[]	getDefaultTokens() Returns the default token a check is interested in.
int[]	getRequiredTokens() The tokens that this check must be registered for.
void	setFormat(Pattern pattern) Setter to specify pattern for strings allowed before the comment.
void	setLegalComment(Pattern legalComment) Setter to define pattern for text allowed in trailing comments.
void	visitToken(DetailAST ast) Called to process a token.

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

clearMessages, destroy, finishTree, getFileContents, getLine, getLines, getMessages, getTabWidth, getTokenNames, init, isCommentNodesRequired, leaveToken, log, log, log, setFileContents, setTabWidth, setTokens

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

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

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

configure, contextualize, getConfiguration, setupChild

Methods inherited from class java.lang.Object

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

Field Detail

MSG_KEY

public static final String MSG_KEY

A key is pointing to the warning message text in "messages.properties" file.

See Also:

Constant Field Values

Constructor Detail

TrailingCommentCheck

public TrailingCommentCheck()

Method Detail

setLegalComment

public void setLegalComment(Pattern legalComment)

Setter to define pattern for text allowed in trailing comments. (This pattern will not be applied to multiline comments and the text of the comment will be trimmed before matching.)

Parameters:

legalComment - pattern to set.

setFormat

public final void setFormat(Pattern pattern)

Setter to specify pattern for strings allowed before the comment.

Parameters:

pattern - a pattern

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:

TokenTypes

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:

TokenTypes

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:

TokenTypes

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

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