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

Class UnnecessaryNullCheckWithInstanceOfCheck

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.UnnecessaryNullCheckWithInstanceOfCheck

All Implemented Interfaces:

Configurable, Contextualizable

public class UnnecessaryNullCheckWithInstanceOfCheck
extends AbstractCheck

Checks for redundant null checks with the instanceof operator.

The instanceof operator inherently returns false when the left operand is null, making explicit null checks redundant in boolean expressions with instanceof.

Since:

10.25.0

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_UNNECESSARY_NULLCHECK	The error message key for reporting unnecessary null checks.

Constructor Summary

Constructors

Constructor	Description
UnnecessaryNullCheckWithInstanceOfCheck()

Method Summary

Modifier and Type	Method	Description
private static Optional<DetailAST>	checkChildForNullCheck(DetailAST currentChild, DetailAST instanceOfNode, DetailAST instanceOfIdent)	Checks a child node for a redundant null check.
private static boolean	containsVariableDereference(DetailAST node, String variableName)	Checks if the given AST node contains a method call or field access on the specified variable.
private static Optional<DetailAST>	findDirectChildContaining(DetailAST parent, DetailAST target)	Finds the direct child of parent that contains the target node.
private static Optional<DetailAST>	findRedundantNullCheck(DetailAST logicalAndNode, DetailAST instanceOfNode)	Finds a redundant null check in a logical AND expression combined with an instanceof check.
private static DetailAST	findTopLevelLogicalExpression(DetailAST node)	Traverses up through LAND and LOR operators to find the top-level logical expression.
private static Optional<DetailAST>	findUnnecessaryNullCheck(DetailAST instanceOfNode)	Checks for an unnecessary null check within a logical AND expression.
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	isAncestorOf(DetailAST node, DetailAST target)	Checks if the given node is an ancestor of (or the same as) the target node.
private static boolean	isNotEqual(DetailAST node)	Checks if the given AST node represents a != (not equal) operator.
private static boolean	isNullCheckRedundant(DetailAST instanceOfIdent, DetailAST nullCheckNode)	Determines if the null check is redundant with the instanceof check.
private static boolean	isNullLiteral(DetailAST node)	Checks if the given AST node is a null literal.
private static Optional<DetailAST>	searchForNullCheck(DetailAST logicalAndNode, DetailAST instanceOfNode, DetailAST instanceOfIdent)	Searches for a redundant null check in the children of a logical AND node.
void	visitToken(DetailAST instanceofNode)	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_UNNECESSARY_NULLCHECK

public static final String MSG_UNNECESSARY_NULLCHECK

The error message key for reporting unnecessary null checks.

See Also:

• Constant Field Values

Constructor Details

UnnecessaryNullCheckWithInstanceOfCheck

public UnnecessaryNullCheckWithInstanceOfCheck()

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 instanceofNode)

Description copied from class: AbstractCheck

Called to process a token.

Overrides:

visitToken in class AbstractCheck

Parameters:

instanceofNode - the token to process

findUnnecessaryNullCheck

private static Optional<DetailAST> findUnnecessaryNullCheck(DetailAST instanceOfNode)

Checks for an unnecessary null check within a logical AND expression.

Parameters:

instanceOfNode - the AST node representing the instanceof expression

Returns:

the identifier if the check is redundant, otherwise null

findTopLevelLogicalExpression

private static DetailAST findTopLevelLogicalExpression(DetailAST node)

Traverses up through LAND and LOR operators to find the top-level logical expression.

Parameters:

node - the starting node

Returns:

the top-level logical expression node

findRedundantNullCheck

private static Optional<DetailAST> findRedundantNullCheck(DetailAST logicalAndNode,
 DetailAST instanceOfNode)

Finds a redundant null check in a logical AND expression combined with an instanceof check.

Parameters:

logicalAndNode - the root node of the logical AND expression

instanceOfNode - the instanceof expression node

Returns:

the AST node representing the redundant null check, or null if not found

searchForNullCheck

private static Optional<DetailAST> searchForNullCheck(DetailAST logicalAndNode,
 DetailAST instanceOfNode,
 DetailAST instanceOfIdent)

Searches for a redundant null check in the children of a logical AND node.

Parameters:

logicalAndNode - the LAND node to search

instanceOfNode - the instanceof expression node

instanceOfIdent - the identifier from the instanceof expression

Returns:

the null check node if found, null otherwise

checkChildForNullCheck

private static Optional<DetailAST> checkChildForNullCheck(DetailAST currentChild,
 DetailAST instanceOfNode,
 DetailAST instanceOfIdent)

Checks a child node for a redundant null check.

Parameters:

currentChild - the child node to check

instanceOfNode - the instanceof expression node

instanceOfIdent - the identifier from the instanceof expression

Returns:

the null check node if found, otherwise empty

findDirectChildContaining

private static Optional<DetailAST> findDirectChildContaining(DetailAST parent,
 DetailAST target)

Finds the direct child of parent that contains the target node.

Parameters:

parent - the parent node

target - the target node to find

Returns:

the direct child containing target, or null if not found

isAncestorOf

private static boolean isAncestorOf(DetailAST node,
 DetailAST target)

Checks if the given node is an ancestor of (or the same as) the target node.

Parameters:

node - the potential ancestor node

target - the target node to check

Returns:

true if node is an ancestor of target, false otherwise

containsVariableDereference

private static boolean containsVariableDereference(DetailAST node,
 String variableName)

Checks if the given AST node contains a method call or field access on the specified variable.

Parameters:

node - the AST node to check

variableName - the name of the variable

Returns:

true if the variable is dereferenced, false otherwise

isNotEqual

private static boolean isNotEqual(DetailAST node)

Checks if the given AST node represents a != (not equal) operator.

Parameters:

node - the AST node to check

Returns:

true if the node is a not equal operator, otherwise false

isNullLiteral

private static boolean isNullLiteral(DetailAST node)

Checks if the given AST node is a null literal.

Parameters:

node - AST node to check

Returns:

true if the node is a null literal, false otherwise

isNullCheckRedundant

private static boolean isNullCheckRedundant(DetailAST instanceOfIdent,
 DetailAST nullCheckNode)

Determines if the null check is redundant with the instanceof check.

Parameters:

instanceOfIdent - the identifier from the instanceof check

nullCheckNode - the node representing the null check

Returns:

true if the null check is unnecessary, false otherwise