EqualsAvoidNullCheck (checkstyle 9.3 API)

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
Modifier and Type Class and Description

private static class EqualsAvoidNullCheck.FieldFrame
Holds the names of fields of a type.
- Nested classes/interfaces inherited from class com.puppycrawl.tools.checkstyle.api.AutomaticBean
  AutomaticBean.OutputStreamOptions

Nested Classes
Modifier and Type	Class and Description
`private static class`	`EqualsAvoidNullCheck.FieldFrame` Holds the names of fields of a type.

Field Summary

Fields
Modifier and Type	Field and Description
`private EqualsAvoidNullCheck.FieldFrame`	`currentFrame` Stack of sets of field names, one for each class of a set of nested classes.
`private static java.lang.String`	`EQUALS` Method name for comparison.
`private boolean`	`ignoreEqualsIgnoreCase` Control whether to ignore `String.equalsIgnoreCase(String)` invocations.
`private static java.lang.String`	`LEFT_CURLY` Curly for comparison.
`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.
`private static java.lang.String`	`STRING` Type name for comparison.

Constructor Summary

Constructors
Constructor and Description

EqualsAvoidNullCheck()

Constructors
Constructor and Description
`EqualsAvoidNullCheck()`

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`private static boolean`	`astTypeIsClassOrEnumOrRecordDef(int tokenType)` Verify that a token is either CLASS_DEF, RECORD_DEF, or ENUM_DEF.
`void`	`beginTree(DetailAST rootAST)` Called before the starting to process a tree.
`private void`	`checkMethodCall(DetailAST methodCall)` Check whether the method call should be violated.
`private static boolean`	`containsAllSafeTokens(DetailAST expr)` Looks for all "safe" Token combinations in the argument expression branch.
`private static boolean`	`containsOneArgument(DetailAST methodCall)` Verify that method call has one argument.
`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.
`private static java.lang.String`	`getFieldType(DetailAST field)` Get field type.
`private static EqualsAvoidNullCheck.FieldFrame`	`getObjectFrame(EqualsAvoidNullCheck.FieldFrame frame)` Get the nearest parent frame which is CLASS_DEF, ENUM_DEF or ENUM_CONST_DEF.
`int[]`	`getRequiredTokens()` The tokens that this check must be registered for.
`private boolean`	`isCalledOnStringFieldOrVariable(DetailAST objCalledOn)` Determine, whether equals method is called on a field of String type.
`private boolean`	`isStringFieldOrVariable(DetailAST objCalledOn)` Whether the field or the variable is of String type.
`private boolean`	`isStringFieldOrVariableFromClass(DetailAST objCalledOn, java.lang.String className)` Whether the field or the variable from the specified class is of String type.
`private boolean`	`isStringFieldOrVariableFromThisInstance(DetailAST objCalledOn)` Whether the field or the variable from THIS instance is of String type.
`private void`	`leaveLiteralNew(DetailAST ast)` Determine whether LITERAL_NEW is an anonymous class definition and leave the frame it is in.
`private void`	`leaveSlist(DetailAST ast)` Determine whether SLIST begins a block, determined by braces.
`void`	`leaveToken(DetailAST ast)` Called after all the child nodes have been process.
`private void`	`processFrame(DetailAST ast)` Process CLASS_DEF, METHOD_DEF, LITERAL_IF, LITERAL_FOR, LITERAL_WHILE, LITERAL_DO, LITERAL_CATCH, LITERAL_TRY, CTOR_DEF, ENUM_DEF, ENUM_CONSTANT_DEF.
`private void`	`processLiteralNew(DetailAST ast)` Determine whether LITERAL_NEW is an anonymous class definition and add it as a frame in this case.
`private void`	`processMethodCall(DetailAST methodCall)` Add the method call to the current frame if it should be processed.
`private void`	`processSlist(DetailAST ast)` Determine whether SLIST begins a block, determined by braces, and add it as a frame in this case.
`void`	`setIgnoreEqualsIgnoreCase(boolean newValue)` Setter to control whether to ignore `String.equalsIgnoreCase(String)` invocations.
`private static DetailAST`	`skipVariableAssign(DetailAST currentAST)` Skips over an inner assign portion of an argument expression.
`private void`	`traverseFieldFrameTree(EqualsAvoidNullCheck.FieldFrame frame)` Traverse the tree of the field frames to check all equals method calls.
`void`	`visitToken(DetailAST ast)` Called to process a token.

Methods inherited from class com.puppycrawl.tools.checkstyle.api.AbstractCheck
clearViolations, destroy, getFileContents, 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.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
  - EQUALS
```
private static final java.lang.String EQUALS
```
    Method name for comparison.
    
    See Also:
    
    Constant Field Values
  - STRING
```
private static final java.lang.String STRING
```
    Type name for comparison.
    
    See Also:
    
    Constant Field Values
  - LEFT_CURLY
```
private static final java.lang.String LEFT_CURLY
```
    Curly for comparison.
    
    See Also:
    
    Constant Field Values
  - ignoreEqualsIgnoreCase
```
private boolean ignoreEqualsIgnoreCase
```
    Control whether to ignore String.equalsIgnoreCase(String) invocations.
  - currentFrame
```
private EqualsAvoidNullCheck.FieldFrame currentFrame
```
    Stack of sets of field names, one for each class of a set of nested classes.
- 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
  - processSlist
```
private void processSlist(DetailAST ast)
```
    Determine whether SLIST begins a block, determined by braces, and add it as a frame in this case.
    
    Parameters:
    
    ast - SLIST ast.
  - leaveSlist
```
private void leaveSlist(DetailAST ast)
```
    Determine whether SLIST begins a block, determined by braces.
    
    Parameters:
    
    ast - SLIST ast.
  - processFrame
```
private void processFrame(DetailAST ast)
```
    Process CLASS_DEF, METHOD_DEF, LITERAL_IF, LITERAL_FOR, LITERAL_WHILE, LITERAL_DO, LITERAL_CATCH, LITERAL_TRY, CTOR_DEF, ENUM_DEF, ENUM_CONSTANT_DEF.
    
    Parameters:
    
    ast - processed ast.
  - processMethodCall
```
private void processMethodCall(DetailAST methodCall)
```
    Add the method call to the current frame if it should be processed.
    
    Parameters:
    
    methodCall - METHOD_CALL ast.
  - processLiteralNew
```
private void processLiteralNew(DetailAST ast)
```
    Determine whether LITERAL_NEW is an anonymous class definition and add it as a frame in this case.
    
    Parameters:
    
    ast - LITERAL_NEW ast.
  - leaveLiteralNew
```
private void leaveLiteralNew(DetailAST ast)
```
    Determine whether LITERAL_NEW is an anonymous class definition and leave the frame it is in.
    
    Parameters:
    
    ast - LITERAL_NEW ast.
  - traverseFieldFrameTree
```
private void traverseFieldFrameTree(EqualsAvoidNullCheck.FieldFrame frame)
```
    Traverse the tree of the field frames to check all equals method calls.
    
    Parameters:
    
    frame - to check method calls in.
  - checkMethodCall
```
private void checkMethodCall(DetailAST methodCall)
```
    Check whether the method call should be violated.
    
    Parameters:
    
    methodCall - method call to check.
  - containsOneArgument
```
private static boolean containsOneArgument(DetailAST methodCall)
```
    Verify that method call has one argument.
    
    Parameters:
    
    methodCall - METHOD_CALL DetailAST
    
    Returns:
    
    true if method call has one argument.
  - containsAllSafeTokens
```
private static boolean containsAllSafeTokens(DetailAST expr)
```
    Looks for all "safe" Token combinations in the argument expression branch.
    
    Parameters:
    
    expr - the argument expression
    
    Returns:
    
    - true if any child matches the set of tokens, false if not
  - skipVariableAssign
```
private static DetailAST skipVariableAssign(DetailAST currentAST)
```
    Skips over an inner assign portion of an argument expression.
    
    Parameters:
    
    currentAST - current token in the argument expression
    
    Returns:
    
    the next relevant token
  - isCalledOnStringFieldOrVariable
```
private boolean isCalledOnStringFieldOrVariable(DetailAST objCalledOn)
```
    Determine, whether equals method is called on a field of String type.
    
    Parameters:
    
    objCalledOn - object ast.
    
    Returns:
    
    true if the object is of String type.
  - isStringFieldOrVariable
```
private boolean isStringFieldOrVariable(DetailAST objCalledOn)
```
    Whether the field or the variable is of String type.
    
    Parameters:
    
    objCalledOn - the field or the variable to check.
    
    Returns:
    
    true if the field or the variable is of String type.
  - isStringFieldOrVariableFromThisInstance
```
private boolean isStringFieldOrVariableFromThisInstance(DetailAST objCalledOn)
```
    Whether the field or the variable from THIS instance is of String type.
    
    Parameters:
    
    objCalledOn - the field or the variable from THIS instance to check.
    
    Returns:
    
    true if the field or the variable from THIS instance is of String type.
  - isStringFieldOrVariableFromClass
```
private boolean isStringFieldOrVariableFromClass(DetailAST objCalledOn,
                                                 java.lang.String className)
```
    Whether the field or the variable from the specified class is of String type.
    
    Parameters:
    
    objCalledOn - the field or the variable from the specified class to check.
    
    className - the name of the class to check in.
    
    Returns:
    
    true if the field or the variable from the specified class is of String type.
  - getObjectFrame
```
private static EqualsAvoidNullCheck.FieldFrame getObjectFrame(EqualsAvoidNullCheck.FieldFrame frame)
```
    Get the nearest parent frame which is CLASS_DEF, ENUM_DEF or ENUM_CONST_DEF.
    
    Parameters:
    
    frame - to start the search from.
    
    Returns:
    
    the nearest parent frame which is CLASS_DEF, ENUM_DEF or ENUM_CONST_DEF.
  - getFieldType
```
private static java.lang.String getFieldType(DetailAST field)
```
    Get field type.
    
    Parameters:
    
    field - to get the type from.
    
    Returns:
    
    type of the field.
  - astTypeIsClassOrEnumOrRecordDef
```
private static boolean astTypeIsClassOrEnumOrRecordDef(int tokenType)
```
    Verify that a token is either CLASS_DEF, RECORD_DEF, or ENUM_DEF.
    
    Parameters:
    
    tokenType - the type of token
    
    Returns:
    
    true if token is of specified type.

Class EqualsAvoidNullCheck

Nested Class Summary

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

Field Summary

Constructor Summary

Method Summary

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

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

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

Methods inherited from class java.lang.Object

Field Detail

MSG_EQUALS_AVOID_NULL

MSG_EQUALS_IGNORE_CASE_AVOID_NULL

EQUALS

STRING

LEFT_CURLY

ignoreEqualsIgnoreCase

currentFrame

Constructor Detail

EqualsAvoidNullCheck

Method Detail

getDefaultTokens

getAcceptableTokens

getRequiredTokens

setIgnoreEqualsIgnoreCase

beginTree

visitToken

leaveToken

finishTree

processSlist

leaveSlist

processFrame

processMethodCall

processLiteralNew

leaveLiteralNew

traverseFieldFrameTree

checkMethodCall

containsOneArgument

containsAllSafeTokens

skipVariableAssign

isCalledOnStringFieldOrVariable

isStringFieldOrVariable

isStringFieldOrVariableFromThisInstance

isStringFieldOrVariableFromClass

getObjectFrame

getFieldType

astTypeIsClassOrEnumOrRecordDef