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

Class MissingNullCaseInSwitchCheck

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.MissingNullCaseInSwitchCheck

All Implemented Interfaces:

Configurable, Contextualizable

public class MissingNullCaseInSwitchCheck
extends AbstractCheck

Checks that a given switch statement or expression that use a reference type in its selector expression has a null case label.

Rationale: switch statements and expressions in Java throw a NullPointerException if the selector expression evaluates to null. As of Java 21, it is now possible to integrate a null check within the switch, eliminating the risk of NullPointerException and simplifies the code as there is no need for an external null check before entering the switch.

See the Java Language Specification for more information about switch statements and expressions.

Specifically, this check validates switch statement or expression that use patterns or strings in their case labels.

Due to Checkstyle not being type-aware, this check cannot validate other reference types, such as enums; syntactically, these are no different from other constants.

Attention: this Check should be activated only on source code that is compiled by jdk21 or above.

Parent is com.puppycrawl.tools.checkstyle.TreeWalker

Violation Message Keys:

• missing.switch.nullcase

Since:

10.18.0

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
MissingNullCaseInSwitchCheck()

Method Summary

Modifier and Type	Method	Description
int[]	getAcceptableTokens()	The configurable token set.
private static List<DetailAST>	getAllCaseLabels(DetailAST switchAST)	Gets all case labels in the given switch AST node.
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	hasLiteralNull(DetailAST caseAST)	Checks if the given case AST node has a null label.
private static boolean	hasPatternCaseLabel(DetailAST caseAST)	Checks if the given case AST node has a pattern variable declaration label or record pattern definition label.
private static boolean	hasStringCaseLabel(DetailAST caseAST)	Checks if the given case contains a string in its label.
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

MissingNullCaseInSwitchCheck

public MissingNullCaseInSwitchCheck()

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

getAllCaseLabels

private static List<DetailAST> getAllCaseLabels(DetailAST switchAST)

Gets all case labels in the given switch AST node.

Parameters:

switchAST - the AST node representing LITERAL_SWITCH

Returns:

a list of all case labels in the switch

hasLiteralNull

private static boolean hasLiteralNull(DetailAST caseAST)

Checks if the given case AST node has a null label.

Parameters:

caseAST - the AST node representing LITERAL_CASE

Returns:

true if the case has null label, false otherwise

hasPatternCaseLabel

private static boolean hasPatternCaseLabel(DetailAST caseAST)

Checks if the given case AST node has a pattern variable declaration label or record pattern definition label.

Parameters:

caseAST - the AST node representing LITERAL_CASE

Returns:

true if case has a pattern in its label

hasStringCaseLabel

private static boolean hasStringCaseLabel(DetailAST caseAST)

Checks if the given case contains a string in its label. It may contain a single string literal or a string literal in a concatenated expression.

Parameters:

caseAST - the AST node representing LITERAL_CASE

Returns:

true if switch block contains a string case label