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

Class UnusedTryResourceShouldBeUnnamedCheck

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.UnusedTryResourceShouldBeUnnamedCheck

All Implemented Interfaces:

Configurable, Contextualizable

public class UnusedTryResourceShouldBeUnnamedCheck
extends AbstractCheck

Ensures that try-with-resources resource variables that are not used are declared as an unnamed variable.

Rationale:

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

Only declared resources inside the try-with-resources parentheses are checked (i.e. var a = lock() or AutoCloseable a = lock()). Resources that are referenced but not declared inside the try (e.g. try (releaser) { }) are never flagged, because those resources cannot be replaced with _.

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

Attention: This check should be activated only on source code that is compiled by jdk21 or higher; unnamed variables came out as a preview feature in Java 21 and became a standard part of the language in Java 22.

Since:

13.5.0

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
private static final class	UnusedTryResourceShouldBeUnnamedCheck.TryResourceDetails	Maintains tracking information about a single try-with-resources resource.

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_RESOURCE_IDENT_PARENTS	Parent token types for an TokenTypes.IDENT that indicate the identifier is not a plain variable reference and should therefore be excluded from "used" detection.
static final String	MSG_UNUSED_TRY_RESOURCE	A key pointing to the warning message text in "messages.properties" file.
private final Deque<Deque<UnusedTryResourceShouldBeUnnamedCheck.TryResourceDetails>>	tryResources	A stack of per-try resource-detail lists.
private static final String	UNNAMED_VARIABLE_IDENTIFIER	The unnamed variable identifier introduced in Java 21.

Constructor Summary

Constructors

Constructor	Description
UnusedTryResourceShouldBeUnnamedCheck()

Method Summary

Modifier and Type	Method	Description
void	beginTree(DetailAST rootAST)	Called before the starting to process a tree.
private static Deque<UnusedTryResourceShouldBeUnnamedCheck.TryResourceDetails>	collectTrackedResources(DetailAST tryAst)	Collects all tracked resources from the RESOURCE_SPECIFICATION of a try-with-resources statement.
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	isObjectReferenceInDot(DetailAST identAst)	Returns true when identAst is the first child of a TokenTypes.DOT node, meaning it is the object reference in an expression such as a.close() — a genuine use of the variable.
private static boolean	isResourceDeclarationIdent(DetailAST identAst)	Returns true when identAst is the variable-name token inside a TokenTypes.RESOURCE node (i.e. the declaration site, not a use).
private static boolean	isResourceUsageCandidate(DetailAST identAst)	Determines whether an TokenTypes.IDENT token is a candidate for being a use of a tracked try resource.
private static boolean	isShadowedByCatchParameter(DetailAST identAst)	Returns true when identAst is shadowed by a catch parameter of an immediately enclosing TokenTypes.LITERAL_CATCH block.
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_TRY_RESOURCE

public static final String MSG_UNUSED_TRY_RESOURCE

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

See Also:

• Constant Field Values

UNNAMED_VARIABLE_IDENTIFIER

private static final String UNNAMED_VARIABLE_IDENTIFIER

The unnamed variable identifier introduced in Java 21.

See Also:

• Constant Field Values

INVALID_RESOURCE_IDENT_PARENTS

private static final int[] INVALID_RESOURCE_IDENT_PARENTS

Parent token types for an TokenTypes.IDENT that indicate the identifier is not a plain variable reference and should therefore be excluded from "used" detection.

tryResources

private final Deque<Deque<UnusedTryResourceShouldBeUnnamedCheck.TryResourceDetails>> tryResources

A stack of per-try resource-detail lists.

Constructor Details

UnusedTryResourceShouldBeUnnamedCheck

public UnusedTryResourceShouldBeUnnamedCheck()

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

collectTrackedResources

private static Deque<UnusedTryResourceShouldBeUnnamedCheck.TryResourceDetails> collectTrackedResources(DetailAST tryAst)

Collects all tracked resources from the RESOURCE_SPECIFICATION of a try-with-resources statement.

Parameters:

tryAst - the TokenTypes.LITERAL_TRY token

Returns:

a deque of UnusedTryResourceShouldBeUnnamedCheck.TryResourceDetails for trackable resources; never null, but may be empty for plain try statements

isResourceUsageCandidate

private static boolean isResourceUsageCandidate(DetailAST identAst)

Determines whether an TokenTypes.IDENT token is a candidate for being a use of a tracked try resource.

Parameters:

identAst - the TokenTypes.IDENT token to inspect

Returns:

true if the token could represent a reference to a resource variable

isShadowedByCatchParameter

private static boolean isShadowedByCatchParameter(DetailAST identAst)

Returns true when identAst is shadowed by a catch parameter of an immediately enclosing TokenTypes.LITERAL_CATCH block.

Parameters:

identAst - the TokenTypes.IDENT token to inspect

Returns:

true if a catch parameter with the same name is in scope

isResourceDeclarationIdent

private static boolean isResourceDeclarationIdent(DetailAST identAst)

Returns true when identAst is the variable-name token inside a TokenTypes.RESOURCE node (i.e. the declaration site, not a use).

Parameters:

identAst - the TokenTypes.IDENT token

Returns:

true if this IDENT is the name in a resource declaration/reference

isObjectReferenceInDot

private static boolean isObjectReferenceInDot(DetailAST identAst)

Returns true when identAst is the first child of a TokenTypes.DOT node, meaning it is the object reference in an expression such as a.close() — a genuine use of the variable.

Parameters:

identAst - the TokenTypes.IDENT token

Returns:

true if the IDENT is the left-hand operand of a dot expression