javax.lang.model.element.AnnotationValueVisitor Maven / Gradle / Ivy
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package javax.lang.model.element;
import java.util.List;
import javax.lang.model.type.TypeMirror;
import javax.lang.model.util.*;
/**
* 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,
* {@code boolean} values versus {@code 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 {@link AnnotationValue#accept accept} method,
* the visitXyz method applicable to that value is
* invoked.
*
* Classes implementing this interface may or may not throw a
* {@code NullPointerException} if the additional parameter {@code p}
* is {@code null}; see documentation of the implementing class for
* details.
*
* @apiNote
* 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 {@link ElementVisitor#visitModule visitModule} in
* {@code ElementVisitor}. The implementations of the default methods
* in this interface will in turn call {@link visitUnknown
* 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 {@linkplain javax.lang.model.util util
* package}. The families follow a naming pattern along the lines of
* {@code FooVisitor}N where N indicates the
* {@linkplain javax.lang.model.SourceVersion source version} the
* visitor is appropriate for.
*
* In particular, a {@code FooVisitor}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), {@code
* FooVisitor}N may also handle that later source version; in
* that case, the {@link
* javax.annotation.processing.SupportedSourceVersion
* SupportedSourceVersion} annotation on the {@code
* FooVisitor}N class will indicate a later version.
*
* When visiting an annotation value representing a language construct
* introduced after source version N, a {@code
* FooVisitor}N will throw an {@link
* 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:
*
*
*
* - {@link AbstractAnnotationValueVisitor6
* AbstractAnnotationValueVisitor}s: Skeletal visitor implementations.
*
*
- {@link SimpleAnnotationValueVisitor6
* SimpleAnnotationValueVisitor}s: Support default actions and a
* default return value.
*
*
*
* @param the return type of this visitor's methods
* @param the type of the additional parameter to this visitor's methods.
* @author Joseph D. Darcy
* @author Scott Seligman
* @author Peter von der Ahé
* @since 1.6
*/
public interface AnnotationValueVisitor {
/**
* Visits an annotation value.
* @param av the value to visit
* @param p a visitor-specified parameter
* @return a visitor-specified result
*/
R visit(AnnotationValue av, P p);
/**
* A convenience method equivalent to {@code visit(av, null)}.
*
* @implSpec The default implementation is {@code visit(av, null)}.
*
* @param av the value to visit
* @return a visitor-specified result
*/
default R visit(AnnotationValue av) {
return visit(av, null);
}
/**
* Visits a {@code boolean} value in an annotation.
* @param b the value being visited
* @param p a visitor-specified parameter
* @return the result of the visit
*/
R visitBoolean(boolean b, P p);
/**
* Visits a {@code byte} value in an annotation.
* @param b the value being visited
* @param p a visitor-specified parameter
* @return the result of the visit
*/
R visitByte(byte b, P p);
/**
* Visits a {@code char} value in an annotation.
* @param c the value being visited
* @param p a visitor-specified parameter
* @return the result of the visit
*/
R visitChar(char c, P p);
/**
* Visits a {@code double} value in an annotation.
* @param d the value being visited
* @param p a visitor-specified parameter
* @return the result of the visit
*/
R visitDouble(double d, P p);
/**
* Visits a {@code float} value in an annotation.
* @param f the value being visited
* @param p a visitor-specified parameter
* @return the result of the visit
*/
R visitFloat(float f, P p);
/**
* Visits an {@code int} value in an annotation.
* @param i the value being visited
* @param p a visitor-specified parameter
* @return the result of the visit
*/
R visitInt(int i, P p);
/**
* Visits a {@code long} value in an annotation.
* @param i the value being visited
* @param p a visitor-specified parameter
* @return the result of the visit
*/
R visitLong(long i, P p);
/**
* Visits a {@code short} value in an annotation.
* @param s the value being visited
* @param p a visitor-specified parameter
* @return the result of the visit
*/
R visitShort(short s, P p);
/**
* Visits a string value in an annotation.
* @param s the value being visited
* @param p a visitor-specified parameter
* @return the result of the visit
*/
R visitString(String s, P p);
/**
* Visits a type value in an annotation.
* @param t the value being visited
* @param p a visitor-specified parameter
* @return the result of the visit
*/
R visitType(TypeMirror t, P p);
/**
* Visits an {@code enum} value in an annotation.
* @param c the value being visited
* @param p a visitor-specified parameter
* @return the result of the visit
*/
R visitEnumConstant(VariableElement c, P p);
/**
* Visits an annotation value in an annotation.
* @param a the value being visited
* @param p a visitor-specified parameter
* @return the result of the visit
*/
R visitAnnotation(AnnotationMirror a, P p);
/**
* Visits an array value in an annotation.
* @param vals the value being visited
* @param p a visitor-specified parameter
* @return the result of the visit
*/
R visitArray(List vals, P p);
/**
* Visits an unknown kind of annotation value.
* This can occur if the language evolves and new kinds
* of value can be stored in an annotation.
* @param av the unknown value being visited
* @param p a visitor-specified parameter
* @return the result of the visit
* @throws UnknownAnnotationValueException
* a visitor implementation may optionally throw this exception
*/
R visitUnknown(AnnotationValue av, P p);
}