com.puppycrawl.tools.checkstyle.checks.coding

Class EqualsAvoidNullCheck

java.lang.Object

com.puppycrawl.tools.checkstyle.api.AutomaticBean

com.puppycrawl.tools.checkstyle.api.AbstractViolationReporter

com.puppycrawl.tools.checkstyle.api.AbstractCheck

com.puppycrawl.tools.checkstyle.checks.coding.EqualsAvoidNullCheck

All Implemented Interfaces:

Configurable, Contextualizable

public class EqualsAvoidNullCheck
extends AbstractCheck

Checks that any combination of String literals is on the left side of an equals() comparison. Also checks for String literals assigned to some field (such as someString.equals(anotherString = "text")).

Rationale: Calling the equals() method on String literals will avoid a potential NullPointerException. Also, it is pretty common to see null checks right before equals comparisons but following this rule such checks are not required.

• Property ignoreEqualsIgnoreCase - Control whether to ignore String.equalsIgnoreCase(String) invocations. Type is boolean. Default value is false.

To configure the check:

 <module name="EqualsAvoidNull"/>
 

Example:

 String nullString = null;
 nullString.equals("My_Sweet_String");            // violation
 "My_Sweet_String".equals(nullString);            // OK
 nullString.equalsIgnoreCase("My_Sweet_String");  // violation
 "My_Sweet_String".equalsIgnoreCase(nullString);  // OK
 

To configure the check to allow ignoreEqualsIgnoreCase:

 <module name="EqualsAvoidNull">
   <property name="ignoreEqualsIgnoreCase" value="true"/>
 </module>
 

Example:

 String nullString = null;
 nullString.equals("My_Sweet_String");            // violation
 "My_Sweet_String".equals(nullString);            // OK
 nullString.equalsIgnoreCase("My_Sweet_String");  // OK
 "My_Sweet_String".equalsIgnoreCase(nullString);  // OK
 

Parent is com.puppycrawl.tools.checkstyle.TreeWalker

Violation Message Keys:

• equals.avoid.null
• equalsIgnoreCase.avoid.null

Since:

5.0

Nested Class Summary

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

AutomaticBean.OutputStreamOptions

Field Summary

Fields

Modifier and Type	Field and Description
static java.lang.String	MSG_EQUALS_AVOID_NULL A key is pointing to the warning message text in "messages.properties" file.
static java.lang.String	MSG_EQUALS_IGNORE_CASE_AVOID_NULL A key is pointing to the warning message text in "messages.properties" file.

Constructor Summary

Constructors

Constructor and Description
EqualsAvoidNullCheck()

Method Summary

Modifier and Type	Method and Description
void	beginTree(DetailAST rootAST) Called before the starting to process a tree.
void	finishTree(DetailAST ast) Called after finished processing 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.
void	leaveToken(DetailAST ast) Called after all the child nodes have been process.
void	setIgnoreEqualsIgnoreCase(boolean newValue) Setter to control whether to ignore String.equalsIgnoreCase(String) invocations.
void	visitToken(DetailAST ast) Called to process a token.

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

clearMessages, destroy, getFileContents, getLine, getLines, getMessages, getTabWidth, getTokenNames, 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.api.AutomaticBean

configure, contextualize, getConfiguration, setupChild

Methods inherited from class java.lang.Object

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

Field Detail

MSG_EQUALS_AVOID_NULL

public static final java.lang.String MSG_EQUALS_AVOID_NULL

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

See Also:

Constant Field Values

MSG_EQUALS_IGNORE_CASE_AVOID_NULL

public static final java.lang.String MSG_EQUALS_IGNORE_CASE_AVOID_NULL

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

See Also:

Constant Field Values

Constructor Detail

EqualsAvoidNullCheck

public EqualsAvoidNullCheck()

Method Detail

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

setIgnoreEqualsIgnoreCase

public void setIgnoreEqualsIgnoreCase(boolean newValue)

Setter to control whether to ignore String.equalsIgnoreCase(String) invocations.

Parameters:

newValue - whether to ignore checking String.equalsIgnoreCase(String).

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

finishTree

public void finishTree(DetailAST ast)

Description copied from class: AbstractCheck

Called after finished processing a tree. Ideal place to report on information collected whilst processing a tree.

Overrides:

finishTree in class AbstractCheck

Parameters:

ast - the root of the tree