AnnotationValueVisitor (Java SE 17 & JDK 17)
Description: declaration: module: java.compiler, package: javax.lang.model.element, interface: AnnotationValueVisitor
Keywords: javax.lang.model.element.AnnotationValueVisitor interface

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 `FooVisitor`N where N indicates the source version the visitor is appropriate for. In particular, a `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), `FooVisitor`N may also handle that later source version; in that case, the `SupportedSourceVersion` annotation on the `FooVisitor`N class will indicate a later version. When visiting an annotation value representing a language construct introduced after source version N, a `FooVisitor`N 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:

  - `AbstractAnnotationValueVisitor`s: Skeletal visitor implementations.
  - `SimpleAnnotationValueVisitor`s: Support default actions and a default return value.
Since:
  1.6

- ## Method Summary

  Modifier and Type
  Method
  Description
  `default R`
  `visit(AnnotationValue av)`
  A convenience method equivalent to `visit(av, null)`.
  `R`
  `visit(AnnotationValue av, P p)`
  Visits an annotation value.
  `R`
  `visitAnnotation(AnnotationMirror a, P p)`
  Visits an annotation value in an annotation.
  `R`
  `visitArray(List<? extends AnnotationValue> vals, P p)`
  Visits an array value in an annotation.
  `R`
  `visitBoolean(boolean b, P p)`
  Visits a `boolean` value in an annotation.
  `R`
  `visitByte(byte b, P p)`
  Visits a `byte` value in an annotation.
  `R`
  `visitChar(char c, P p)`
  Visits a `char` value in an annotation.
  `R`
  `visitDouble(double d, P p)`
  Visits a `double` value in an annotation.
  `R`
  `visitEnumConstant(VariableElement c, P p)`
  Visits an `enum` value in an annotation.
  `R`
  `visitFloat(float f, P p)`
  Visits a `float` value in an annotation.
  `R`
  `visitInt(int i, P p)`
  Visits an `int` value in an annotation.
  `R`
  `visitLong(long i, P p)`
  Visits a `long` value in an annotation.
  `R`
  `visitShort(short s, P p)`
  Visits a `short` value in an annotation.
  `R`
  `visitString(String s, P p)`
  Visits a string value in an annotation.
  `R`
  `visitType(TypeMirror t, P p)`
  Visits a type value in an annotation.
  `R`
  `visitUnknown(AnnotationValue av, P p)`
  Visits an unknown kind of annotation value.

- ## Method Details

  - ### visit

    R visit(AnnotationValue av, P p)
    Visits an annotation value.
    Parameters:
      `av` - the value to visit
      `p` - a visitor-specified parameter
    Returns:
      a visitor-specified result

  - ### visit

    default R visit(AnnotationValue av)
    A convenience method equivalent to `visit(av, null)`.
    Implementation Requirements:
      The default implementation is `visit(av, null)`.
    Parameters:
      `av` - the value to visit
    Returns:
      a visitor-specified result

  - ### visitBoolean

    R visitBoolean(boolean b, P p)
    Visits a `boolean` value in an annotation.
    Parameters:
      `b` - the value being visited
      `p` - a visitor-specified parameter
    Returns:
      the result of the visit

  - ### visitByte

    R visitByte(byte b, P p)
    Visits a `byte` value in an annotation.
    Parameters:
      `b` - the value being visited
      `p` - a visitor-specified parameter
    Returns:
      the result of the visit

  - ### visitChar

    R visitChar(char c, P p)
    Visits a `char` value in an annotation.
    Parameters:
      `c` - the value being visited
      `p` - a visitor-specified parameter
    Returns:
      the result of the visit

  - ### visitDouble

    R visitDouble(double d, P p)
    Visits a `double` value in an annotation.
    Parameters:
      `d` - the value being visited
      `p` - a visitor-specified parameter
    Returns:
      the result of the visit

  - ### visitFloat

    R visitFloat(float f, P p)
    Visits a `float` value in an annotation.
    Parameters:
      `f` - the value being visited
      `p` - a visitor-specified parameter
    Returns:
      the result of the visit

  - ### visitInt

    R visitInt(int i, P p)
    Visits an `int` value in an annotation.
    Parameters:
      `i` - the value being visited
      `p` - a visitor-specified parameter
    Returns:
      the result of the visit

  - ### visitLong

    R visitLong(long i, P p)
    Visits a `long` value in an annotation.
    Parameters:
      `i` - the value being visited
      `p` - a visitor-specified parameter
    Returns:
      the result of the visit

  - ### visitShort

    R visitShort(short s, P p)
    Visits a `short` value in an annotation.
    Parameters:
      `s` - the value being visited
      `p` - a visitor-specified parameter
    Returns:
      the result of the visit

  - ### visitString

    R visitString(String s, P p)
    Visits a string value in an annotation.
    Parameters:
      `s` - the value being visited
      `p` - a visitor-specified parameter
    Returns:
      the result of the visit

  - ### visitType

    R visitType(TypeMirror t, P p)
    Visits a type value in an annotation.
    Parameters:
      `t` - the value being visited
      `p` - a visitor-specified parameter
    Returns:
      the result of the visit

  - ### visitEnumConstant

    R visitEnumConstant(VariableElement c, P p)
    Visits an `enum` value in an annotation.
    Parameters:
      `c` - the value being visited
      `p` - a visitor-specified parameter
    Returns:
      the result of the visit

  - ### visitAnnotation

    R visitAnnotation(AnnotationMirror a, P p)
    Visits an annotation value in an annotation.
    Parameters:
      `a` - the value being visited
      `p` - a visitor-specified parameter
    Returns:
      the result of the visit

  - ### visitArray

    R visitArray(List<? extends AnnotationValue> vals, P p)
    Visits an array value in an annotation.
    Parameters:
      `vals` - the value being visited
      `p` - a visitor-specified parameter
    Returns:
      the result of the visit

  - ### visitUnknown

    R visitUnknown(AnnotationValue av, 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.
    Parameters:
      `av` - the unknown value being visited
      `p` - a visitor-specified parameter
    Returns:
      the result of the visit
    Throws:
      `UnknownAnnotationValueException` - a visitor implementation may optionally throw this exception