- Type Parameters:
R
- the return type of this visitor's methods. UseVoid
for visitors that do not need to return results.P
- the type of the additional parameter to this visitor's methods. UseVoid
for visitors that do not need an additional parameter.
- All Known Implementing Classes:
AbstractElementVisitor14
,AbstractElementVisitor6
,AbstractElementVisitor7
,AbstractElementVisitor8
,AbstractElementVisitor9
,ElementKindVisitor14
,ElementKindVisitor6
,ElementKindVisitor7
,ElementKindVisitor8
,ElementKindVisitor9
,ElementScanner14
,ElementScanner6
,ElementScanner7
,ElementScanner8
,ElementScanner9
,SimpleElementVisitor14
,SimpleElementVisitor6
,SimpleElementVisitor7
,SimpleElementVisitor8
,SimpleElementVisitor9
public interface ElementVisitor<R,P>
accept
method, the visitXyz
method most applicable
to that element is invoked.
Classes implementing this interface may or may not throw a
NullPointerException
if the additional parameter p
is null
; see documentation of the implementing class for
details.
- API Note:
- WARNING: It is possible that methods will be added
to this interface to accommodate new, currently unknown, language
structures added to future versions of the Java programming
language.
Such additions have already occurred to support language features
added after this API was introduced.
Visitor classes directly implementing this interface may be source
incompatible with future versions of the platform. To avoid this
source incompatibility, visitor implementations are encouraged to
instead extend the appropriate abstract visitor class that
implements this interface. However, an API should generally use
this visitor interface as the type for parameters, return type,
etc. rather than one of the abstract classes.
Methods to accommodate new language constructs are expected to be added as default methods to provide strong source compatibility, as done for
visitModule
. The implementations of the default methods will in turn callvisitUnknown
, behavior that will be overridden in concrete visitors supporting the source version with the new language construct.There are several families of classes implementing this visitor interface in the util package. The families follow a naming pattern along the lines of
FooVisitor
N where N indicates the source version the visitor is appropriate for. In particular, aFooVisitor
N is expected to handle all language constructs present in source version N. If there are no new language constructs added in version N + 1 (or subsequent releases),FooVisitor
N may also handle that later source version; in that case, theSupportedSourceVersion
annotation on theFooVisitor
N class will indicate a later version. When visiting an element representing a language construct introduced after source version N, aFooVisitor
N will throw anUnknownElementException
unless that behavior is overridden.When choosing which member of a visitor family to subclass, subclassing the most recent one increases the range of source versions covered. When choosing which visitor family to subclass, consider their built-in capabilities:
AbstractElementVisitor
s: Skeletal visitor implementations.SimpleElementVisitor
s: Support default actions and a default return value.ElementKindVisitor
s: Visit methods provided on a per-kind granularity as some categories of elements can have more than one kind.ElementScanner
s: Scanners are visitors which traverse an element and the elements enclosed by it and associated with it.
- Since:
- 1.6
-
Method Summary
Modifier and Type Method Description default R
visit(Element e)
A convenience method equivalent tovisit(e, null)
.R
visit(Element e, P p)
Visits an element.R
visitExecutable(ExecutableElement e, P p)
Visits an executable element.default R
visitModule(ModuleElement e, P p)
Visits a module element.R
visitPackage(PackageElement e, P p)
Visits a package element.default R
visitRecordComponent(RecordComponentElement e, P p)
Associated with records, a preview feature of the Java language.
Visits a record component element.R
visitType(TypeElement e, P p)
Visits a type element.R
visitTypeParameter(TypeParameterElement e, P p)
Visits a type parameter element.R
visitUnknown(Element e, P p)
Visits an unknown kind of element.R
visitVariable(VariableElement e, P p)
Visits a variable element.
-
Method Details
-
visit
Visits an element.- Parameters:
e
- the element to visitp
- a visitor-specified parameter- Returns:
- a visitor-specified result
-
visit
A convenience method equivalent tovisit(e, null)
.- Implementation Requirements:
- The default implementation is
visit(e, null)
. - Parameters:
e
- the element to visit- Returns:
- a visitor-specified result
-
visitPackage
Visits a package element.- Parameters:
e
- the element to visitp
- a visitor-specified parameter- Returns:
- a visitor-specified result
-
visitType
Visits a type element.- Parameters:
e
- the element to visitp
- a visitor-specified parameter- Returns:
- a visitor-specified result
-
visitVariable
Visits a variable element.- Parameters:
e
- the element to visitp
- a visitor-specified parameter- Returns:
- a visitor-specified result
-
visitExecutable
Visits an executable element.- Parameters:
e
- the element to visitp
- a visitor-specified parameter- Returns:
- a visitor-specified result
-
visitTypeParameter
Visits a type parameter element.- Parameters:
e
- the element to visitp
- a visitor-specified parameter- Returns:
- a visitor-specified result
-
visitUnknown
Visits an unknown kind of element. This can occur if the language evolves and new kinds of elements are added to theElement
hierarchy.- Parameters:
e
- the element to visitp
- a visitor-specified parameter- Returns:
- a visitor-specified result
- Throws:
UnknownElementException
- a visitor implementation may optionally throw this exception
-
visitModule
Visits a module element.- Implementation Requirements:
- The default implementation visits a
ModuleElement
by callingvisitUnknown(e, p)
. - Parameters:
e
- the element to visitp
- a visitor-specified parameter- Returns:
- a visitor-specified result
- Since:
- 9
-
visitRecordComponent
This method is associated with records, a preview feature of the Java language. Preview features may be removed in a future release, or upgraded to permanent features of the Java language.
Visits a record component element.- Implementation Requirements:
- The default implementation visits a
RecordComponentElement
by callingvisitUnknown(e, p)
. - Parameters:
e
- the element to visitp
- a visitor-specified parameter- Returns:
- a visitor-specified result
- Since:
- 14
-