Module java.compiler
Package javax.lang.model.element

Interface AnnotationValueVisitor<R,P>

Type Parameters:
R - the return type of this visitor's methods
P - the type of the additional parameter to this visitor's methods.
All Known Implementing Classes:
AbstractAnnotationValueVisitor14, AbstractAnnotationValueVisitor6, AbstractAnnotationValueVisitor7, AbstractAnnotationValueVisitor8, AbstractAnnotationValueVisitor9, SimpleAnnotationValueVisitor14, SimpleAnnotationValueVisitor6, SimpleAnnotationValueVisitor7, SimpleAnnotationValueVisitor8, SimpleAnnotationValueVisitor9
public interface AnnotationValueVisitor<R,P>
A visitor of the values of annotation interface elements, using a variant of the visitor design pattern. Unlike a standard visitor which dispatches based on the concrete type of a member of a type hierarchy, this visitor dispatches based on the type of data stored; there are no distinct subclasses for storing, for example, boolean values versus int values. Classes implementing this interface are used to operate on a value when the type of that value is unknown at compile time. When a visitor is passed to a value's accept method, the visitXyz method applicable to that value 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 in another visitor interface in this package 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 in ElementVisitor. The implementations of the default methods in this interface will in turn call visitUnknown, 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 FooVisitorN where N indicates the source version the visitor is appropriate for. In particular, a FooVisitorN 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), FooVisitorN may also handle that later source version; in that case, the SupportedSourceVersion annotation on the FooVisitorN class will indicate a later version. When visiting an annotation value representing a language construct introduced after source version N, a FooVisitorN will throw an UnknownAnnotationValueException 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:

Since:
1.6