Class UnusedLambdaParameterShouldBeUnnamedCheck

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.coding.UnusedLambdaParameterShouldBeUnnamedCheck
All Implemented Interfaces:
Configurable, Contextualizable
public class UnusedLambdaParameterShouldBeUnnamedCheck extends AbstractCheck
Ensures that lambda parameters that are not used are declared as an unnamed variable.

Rationale:

  • Improves code readability by clearly indicating which parameters are unused.
  • Follows Java conventions for denoting unused parameters with an underscore (_).

See the Java Language Specification for more information about unnamed variables.

Attention: Unnamed variables are available as a preview feature in Java 21, and became an official part of the language in Java 22. This check should be activated only on source code which meets those requirements.

Since:
10.18.0

  • Field Details

    • MSG_UNUSED_LAMBDA_PARAMETER

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

    • INVALID_LAMBDA_PARAM_IDENT_PARENTS

      private static final int[] INVALID_LAMBDA_PARAM_IDENT_PARENTS
      Invalid parents of the lambda parameter identifier. These are tokens that can not be parents for a lambda parameter identifier.

    • lambdaParameters

      private final Deque<UnusedLambdaParameterShouldBeUnnamedCheck.LambdaParameterDetails> lambdaParameters
      Keeps track of the lambda parameters in a block.

  • Constructor Details

    • UnusedLambdaParameterShouldBeUnnamedCheck

      public UnusedLambdaParameterShouldBeUnnamedCheck()

  • 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:

    • 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

    • 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

    • leaveToken

      public void leaveToken(DetailAST ast)
      Description copied from class: AbstractCheck
      Called after all the child nodes have been process.
      Overrides:
      leaveToken in class AbstractCheck
      Parameters:
      ast - the token leaving

    • isLambdaParameterIdentifierCandidate

      private static boolean isLambdaParameterIdentifierCandidate(DetailAST identifierAst)
      Visit ast of type TokenTypes.IDENT and check if it is a candidate for a lambda parameter identifier.
      Parameters:
      identifierAst - token representing TokenTypes.IDENT
      Returns:
      true if the given TokenTypes.IDENT could be a lambda parameter identifier

    • hasValidParentToken

      private static boolean hasValidParentToken(DetailAST identifierAst)
      Check if the given TokenTypes.IDENT has a valid parent token. A valid parent token is a token that can be a parent for a lambda parameter identifier.
      Parameters:
      identifierAst - token representing TokenTypes.IDENT
      Returns:
      true if the given TokenTypes.IDENT has a valid parent token

    • isMethodInvocation

      private static boolean isMethodInvocation(DetailAST identAst)
      Check if the given TokenTypes.IDENT is a child of a dot operator and is a candidate for lambda parameter.
      Parameters:
      identAst - token representing TokenTypes.IDENT
      Returns:
      true if the given TokenTypes.IDENT is a child of a dot operator and a candidate for lambda parameter.

    • isLeftHandOfAssignment

      private static boolean isLeftHandOfAssignment(DetailAST identAst)
      Check if the given TokenTypes.IDENT is a left hand side value.
      Parameters:
      identAst - token representing TokenTypes.IDENT
      Returns:
      true if the given TokenTypes.IDENT is a left hand side value.