Class CovariantEqualsCheck
- 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.CovariantEqualsCheck
-
- All Implemented Interfaces:
Configurable
,Contextualizable
public class CovariantEqualsCheck extends AbstractCheck
Checks that classes and records which define a covariantequals()
method also override methodequals(Object)
.Covariant
equals()
- method that is similar toequals(Object)
, but with a covariant parameter type (any subtype of Object).Notice: the enums are also checked, even though they cannot override
equals(Object)
. The reason is to point out that implementingequals()
in enums is considered an awful practice: it may cause having two different enum values that are equal using covariant enum method, and not equal when compared normally.Inspired by Finding Bugs is Easy, chapter '4.5 Bad Covariant Definition of Equals (Eq)':
Java classes and records may override the
equals(Object)
method to define a predicate for object equality. This method is used by many of the Java runtime library classes; for example, to implement generic containers.Programmers sometimes mistakenly use the type of their class
Foo
as the type of the parameter toequals()
:public boolean equals(Foo obj) {...}
This covariant version of
equals()
does not override the version in theObject
class, and it may lead to unexpected behavior at runtime, especially if the class is used with one of the standard collection classes which expect that the standardequals(Object)
method is overridden.This kind of bug is not obvious because it looks correct, and in circumstances where the class is accessed through the references of the class type (rather than a supertype), it will work correctly. However, the first time it is used in a container, the behavior might be mysterious. For these reasons, this type of bug can elude testing and code inspections.
Parent is
com.puppycrawl.tools.checkstyle.TreeWalker
Violation Message Keys:
-
covariant.equals
- Since:
- 3.2
-
-
Nested Class Summary
-
Nested classes/interfaces inherited from class com.puppycrawl.tools.checkstyle.AbstractAutomaticBean
AbstractAutomaticBean.OutputStreamOptions
-
-
Field Summary
Fields Modifier and Type Field Description private Set<DetailAST>
equalsMethods
Set of equals method definitions.static String
MSG_KEY
A key is pointing to the warning message text in "messages.properties" file.
-
Constructor Summary
Constructors Constructor Description CovariantEqualsCheck()
-
Method Summary
All Methods Static Methods Instance Methods Concrete Methods Modifier and Type Method Description 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
isFirstParameterObject(DetailAST methodDefAst)
Tests whether a method's first parameter is an Object.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
-
-
-
-
Field Detail
-
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
-
equalsMethods
private final Set<DetailAST> equalsMethods
Set of equals method definitions.
-
-
Constructor Detail
-
CovariantEqualsCheck
public CovariantEqualsCheck()
-
-
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 classAbstractCheck
- Returns:
- the default tokens
- 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 classAbstractCheck
- Returns:
- the token set this must be registered for.
- 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 classAbstractCheck
- Returns:
- the token set this check is designed for.
- See Also:
TokenTypes
-
visitToken
public void visitToken(DetailAST ast)
Description copied from class:AbstractCheck
Called to process a token.- Overrides:
visitToken
in classAbstractCheck
- Parameters:
ast
- the token to process
-
isFirstParameterObject
private static boolean isFirstParameterObject(DetailAST methodDefAst)
Tests whether a method's first parameter is an Object.- Parameters:
methodDefAst
- the method definition AST to test. Precondition: ast is a TokenTypes.METHOD_DEF node.- Returns:
- true if ast has first parameter of type Object.
-
-