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

Class ExpressionOverBlockLambdaCheck

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.ExpressionOverBlockLambdaCheck

All Implemented Interfaces:

Configurable, Contextualizable

public class ExpressionOverBlockLambdaCheck
extends AbstractCheck

Checks that expression lambdas are used instead of single-line block lambdas where possible.

Rationale: According to the OpenJDK Java Style Guidelines (and general modern Java conventions), expression lambdas are preferred over single-line block lambdas for readability and conciseness.

A single-line block lambda is a lambda whose body is a block ({...}) that fits on a single line and contains only one statement that could be written as an expression lambda.

Since:

14.1.0

Nested Class Summary

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

AbstractAutomaticBean.OutputStreamOptions

Field Summary

Fields

Modifier and Type	Field	Description
static final String	MSG_KEY	A key is pointing to the warning message text in "messages.properties" file.

Constructor Summary

Constructors

Constructor	Description
ExpressionOverBlockLambdaCheck()	Creates a new ExpressionOverBlockLambdaCheck instance.

Method Summary

Modifier and Type	Method	Description
private static DetailAST	findSingleStatement(DetailAST slist)	Finds the single statement in a block lambda body, or returns null if there are zero or multiple statements.
int[]	getAcceptableTokens()	The configurable token set.
int[]	getDefaultTokens()	Returns the default token a check is interested in.
private static DetailAST	getLastLambdaToken(DetailAST lambda)	Gets the last token in a lambda.
int[]	getRequiredTokens()	The tokens that this check must be registered for.
private static boolean	hasReturnExpression(DetailAST literalReturn)	Checks if a return statement has an expression (not bare return).
private static boolean	isConvertibleToExpressionLambda(DetailAST statement)	Checks if the statement in a block lambda can be rewritten as an expression lambda.
private static boolean	isSingleLineLambda(DetailAST lambda)	Checks if a lambda is single-line.
private static boolean	isSwitchRuleLambda(DetailAST lambda)	Checks if the lambda is a switch rule lambda.
void	visitToken(DetailAST ast)	Called to process a token.

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

beginTree, clearViolations, destroy, finishTree, getFileContents, getFilePath, getLine, getLineCodePoints, getLines, getTabWidth, getTokenNames, getViolations, init, isCommentNodesRequired, leaveToken, 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_KEY

public static final String MSG_KEY

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

See Also:

• Constant Field Values

Constructor Details

ExpressionOverBlockLambdaCheck

public ExpressionOverBlockLambdaCheck()

Creates a new ExpressionOverBlockLambdaCheck instance.

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

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

isSwitchRuleLambda

private static boolean isSwitchRuleLambda(DetailAST lambda)

Checks if the lambda is a switch rule lambda.

Parameters:

lambda - the lambda AST node

Returns:

true if the lambda is part of a switch rule

isSingleLineLambda

private static boolean isSingleLineLambda(DetailAST lambda)

Checks if a lambda is single-line.

Parameters:

lambda - the lambda AST node

Returns:

true if the lambda fits on a single line

getLastLambdaToken

private static DetailAST getLastLambdaToken(DetailAST lambda)

Gets the last token in a lambda.

Parameters:

lambda - the lambda AST node

Returns:

the last token in the lambda

findSingleStatement

private static DetailAST findSingleStatement(DetailAST slist)

Finds the single statement in a block lambda body, or returns null if there are zero or multiple statements.

Parameters:

slist - the SLIST node (lambda body)

Returns:

the single statement, or null if not exactly one

isConvertibleToExpressionLambda

private static boolean isConvertibleToExpressionLambda(DetailAST statement)

Checks if the statement in a block lambda can be rewritten as an expression lambda.

Parameters:

statement - the statement node

Returns:

true if the statement can be converted to an expression lambda

hasReturnExpression

private static boolean hasReturnExpression(DetailAST literalReturn)

Checks if a return statement has an expression (not bare return).

Parameters:

literalReturn - the LITERAL_RETURN node

Returns:

true if the return statement has an expression