Package com.puppycrawl.tools.checkstyle.checks.naming

Class GoogleNonConstantFieldNameCheck

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.naming.GoogleNonConstantFieldNameCheck
All Implemented Interfaces:
Configurable, Contextualizable
public class GoogleNonConstantFieldNameCheck extends AbstractCheck
Checks that non-constant field names conform to the Google Java Style Guide for non-constant field naming.

This check enforces Google's specific non-constant field naming requirements:

  • Non-constant field names must start with a lowercase letter and use uppercase letters for word boundaries.
  • Underscores may be used to separate adjacent numbers (e.g., version numbers like guava33_4_5), but NOT between letters and digits.

Static fields are skipped because Checkstyle cannot determine type immutability to distinguish constants from non-constants. Fields in interfaces and annotations are also skipped because they are implicitly public static final (constants)

Since:
13.3.0

  • Field Details

    • MSG_KEY_INVALID_FORMAT

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

    • NON_CONSTANT_FIELD_NAME_PATTERN

      private static final Pattern NON_CONSTANT_FIELD_NAME_PATTERN
      Pattern for valid non-constant field name in Google style. Format: start with lowercase, have at least 2 chars, optionally followed by numbering suffix.

      Explanation:

      • ^(?![a-z]$) - Negative lookahead: cannot be single lowercase char
      • (?![a-z][A-Z]) - Negative lookahead: cannot be like "fO"
      • [a-z] - Must start with lowercase
      • [a-z0-9]*+ - Followed by lowercase or digits
      • (?:[A-Z][a-z0-9]*+)*+ - CamelCase humps (uppercase followed by lowercase)
      • $ - End of string (numbering suffix validated separately)

    • NUMBERING_SUFFIX_PATTERN

      private static final Pattern NUMBERING_SUFFIX_PATTERN
      Pattern to strip trailing numbering suffix (underscore followed by digits).

    • INVALID_UNDERSCORE_PATTERN

      private static final Pattern INVALID_UNDERSCORE_PATTERN
      Pattern to detect invalid underscore usage: leading, trailing, consecutive, or between letter-letter, letter-digit, or digit-letter combinations.

  • Constructor Details

  • Method Details

    • 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

    • getIdent

      private static DetailAST getIdent(DetailAST ast)
      Returns the IDENT node of the given AST.
      Parameters:
      ast - the AST node
      Returns:
      the IDENT child node

    • shouldCheckFieldName

      private static boolean shouldCheckFieldName(DetailAST ast)
      Checks if this field should be validated. Returns true for instance fields only. Static fields are excluded because Checkstyle cannot determine type immutability. Local variables and interface/annotation fields are also excluded.
      Parameters:
      ast - the VARIABLE_DEF AST node
      Returns:
      true if this variable should be checked

    • getModifiers

      private static DetailAST getModifiers(DetailAST ast)
      Returns the MODIFIERS node of the given AST. The MODIFIERS node is always present in the AST for type, method, and field declarations, even when no modifiers are explicitly written in code (e.g., int x; still has an empty MODIFIERS node).
      Parameters:
      ast - the AST node
      Returns:
      the MODIFIERS child node

    • validateNonConstantFieldName

      private void validateNonConstantFieldName(DetailAST nameAst, String fieldName)
      Validates a non-constant field name according to Google style.
      Parameters:
      nameAst - the IDENT AST node containing the field name
      fieldName - the field name string