public class CovariantEqualsCheck extends AbstractCheck
Checks that classes which define a covariant equals() method
also override method equals(Object).
Covariant equals() - method that is similar to equals(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 implementing equals() 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 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 to equals():
public boolean equals(Foo obj) {...}
This covariant version of equals() does not override the version in
the Object 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 standard equals(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.
To configure the check:
<module name="CovariantEquals"/>
For example:
class Test {
public boolean equals(Test i) { // violation
return false;
}
}
The same class without violations:
class Test {
public boolean equals(Test i) { // no violation
return false;
}
public boolean equals(Object i) {
return false;
}
}
Parent is com.puppycrawl.tools.checkstyle.TreeWalker
Violation Message Keys:
covariant.equals
AutomaticBean.OutputStreamOptions| Modifier and Type | Field and Description |
|---|---|
static String |
MSG_KEY
A key is pointing to the warning message text in "messages.properties"
file.
|
| Constructor and Description |
|---|
CovariantEqualsCheck() |
| Modifier and Type | Method and 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.
|
void |
visitToken(DetailAST ast)
Called to process a token.
|
beginTree, clearMessages, destroy, finishTree, getFileContents, getLine, getLines, getMessages, getTabWidth, getTokenNames, init, isCommentNodesRequired, leaveToken, log, log, log, setFileContents, setTabWidth, setTokensfinishLocalSetup, getCustomMessages, getId, getMessageBundle, getSeverity, getSeverityLevel, setId, setSeverityconfigure, contextualize, getConfiguration, setupChildpublic static final String MSG_KEY
public CovariantEqualsCheck()
public int[] getDefaultTokens()
AbstractCheckgetDefaultTokens in class AbstractCheckTokenTypespublic int[] getRequiredTokens()
AbstractCheckgetRequiredTokens in class AbstractCheckTokenTypespublic int[] getAcceptableTokens()
AbstractCheckgetAcceptableTokens in class AbstractCheckTokenTypespublic void visitToken(DetailAST ast)
AbstractCheckvisitToken in class AbstractCheckast - the token to processCopyright © 2001–2020. All rights reserved.