Package com.puppycrawl.tools.checkstyle.checks.coding

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.

Parent is com.puppycrawl.tools.checkstyle.TreeWalker

Violation Message Keys:

• unused.lambda.parameter

Since:

10.18.0

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
private static final class	UnusedLambdaParameterShouldBeUnnamedCheck.LambdaParameterDetails	Maintains information about the lambda parameter.

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

AbstractAutomaticBean.OutputStreamOptions

Field Summary

Fields

Modifier and Type	Field	Description
private static final int[]	INVALID_LAMBDA_PARAM_IDENT_PARENTS	Invalid parents of the lambda parameter identifier.
private final Deque<UnusedLambdaParameterShouldBeUnnamedCheck.LambdaParameterDetails>	lambdaParameters	Keeps track of the lambda parameters in a block.
static final String	MSG_UNUSED_LAMBDA_PARAMETER	A key is pointing to the warning message text in "messages.properties" file.

Constructor Summary

Constructors

Constructor	Description
UnusedLambdaParameterShouldBeUnnamedCheck()

Method Summary

Modifier and Type	Method	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.
private static boolean	hasValidParentToken(DetailAST identifierAst)	Check if the given TokenTypes.IDENT has a valid parent token.
private static boolean	isLambdaParameterIdentifierCandidate(DetailAST identifierAst)	Visit ast of type TokenTypes.IDENT and check if it is a candidate for a lambda parameter identifier.
private static boolean	isLeftHandOfAssignment(DetailAST identAst)	Check if the given TokenTypes.IDENT is a left hand side value.
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.
void	leaveToken(DetailAST ast)	Called after all the child nodes have been process.
void	visitToken(DetailAST ast)	Called to process a token.

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

clearViolations, destroy, finishTree, getFileContents, getFilePath, getLine, getLineCodePoints, getLines, getTabWidth, getTokenNames, getViolations, init, isCommentNodesRequired, 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.AbstractAutomaticBean

configure, contextualize, getConfiguration, setupChild

Methods inherited from class java.lang.Object

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

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:

• Constant Field Values

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:

• 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

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.