Package com.puppycrawl.tools.checkstyle.checks

Class TrailingCommentCheck

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.TrailingCommentCheck
All Implemented Interfaces:
Configurable, Contextualizable
public class TrailingCommentCheck extends AbstractCheck
The check to ensure that lines with code do not end with comment. 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. Type is java.util.regex.Pattern. Default value is null.

Parent is com.puppycrawl.tools.checkstyle.TreeWalker

Violation Message Keys:

  • trailing.comments
Since:
3.4

  • Field Details

    • MSG_KEY

      public static final String MSG_KEY
      A key is pointing to the warning message text in "messages.properties" file.
      See Also:

    • FORMAT_LINE

      private static final Pattern FORMAT_LINE
      Specify pattern for strings to be formatted without comment specifiers.

    • legalComment

      private Pattern legalComment
      Define pattern for text allowed in trailing comments. This pattern will not be applied to multiline comments.

    • format

      private Pattern format
      Specify pattern for strings allowed before the comment.

  • Constructor Details

  • Method Details

    • 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.
      Parameters:
      legalComment - pattern to set.
      Since:
      4.2

    • setFormat

      public final void setFormat(Pattern pattern)
      Setter to specify pattern for strings allowed before the comment.
      Parameters:
      pattern - a pattern
      Since:
      3.4

    • isCommentNodesRequired

      public boolean isCommentNodesRequired()
      Description copied from class: AbstractCheck
      Whether comment nodes are required or not.
      Overrides:
      isCommentNodesRequired in class AbstractCheck
      Returns:
      false as a default value.

    • 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:

    • 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:

    • 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:

    • 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

    • checkSingleLineComment

      private void checkSingleLineComment(DetailAST ast)
      Checks if single-line comment is legal.
      Parameters:
      ast - Detail ast element to be checked.

    • checkBlockComment

      private void checkBlockComment(DetailAST ast)
      Method to check if block comment is in correct format.
      Parameters:
      ast - Detail ast element to be checked.

    • isLegalCommentContent

      private boolean isLegalCommentContent(String commentContent)
      Checks if given comment content is legal.
      Parameters:
      commentContent - comment content to check.
      Returns:
      true if the content is legal.