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package javax.lang.model.element;


import java.util.List;

import javax.lang.model.type.TypeMirror;



A visitor of the values of annotation type 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. 
 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.  Therefore, 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.

Note that methods to accommodate new language constructs could
be added in a source compatible way if they were added as
default methods. However, default methods are only available on Java SE 8 and higher releases and the 
javax.lang.model.* packages bundled in Java SE 8 were required to also be runnable on Java SE 7. Therefore, default methods were not used when extending javax.lang.model.* to cover Java SE 8 language features. However, default methods are used in subsequent revisions of the javax.lang.model.* packages that are only required to run on Java SE 8 and higher platform versions. 
Author:Joseph D. Darcy, Scott Seligman, Peter von der Ahé
Type parameters:
  • <R> – the return type of this visitor's methods
  • <P> – the type of the additional parameter to this visitor's methods.
Since:1.6
/**
 * A visitor of the values of annotation type 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 <code>visit<i>Xyz</i></code> method applicable to that value is
 * invoked.
 *
 * <p> 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.
 *
 * <p> <b>WARNING:</b> 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&trade; programming
 * language.  Therefore, 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.
 *
 * <p>Note that methods to accommodate new language constructs could
 * be added in a source <em>compatible</em> way if they were added as
 * <em>default methods</em>.  However, default methods are only
 * available on Java SE 8 and higher releases and the {@code
 * javax.lang.model.*} packages bundled in Java SE 8 were required to
 * also be runnable on Java SE 7.  Therefore, default methods
 * were <em>not</em> used when extending {@code javax.lang.model.*}
 * to cover Java SE 8 language features.  However, default methods
 * are used in subsequent revisions of the {@code javax.lang.model.*}
 * packages that are only required to run on Java SE 8 and higher
 * platform versions.
 *
 * @param <R> the return type of this visitor's methods
 * @param <P> the type of the additional parameter to this visitor's methods.
 * @author Joseph D. Darcy
 * @author Scott Seligman
 * @author Peter von der Ah&eacute;
 * @since 1.6
 */
public interface AnnotationValueVisitor<R, P> {
    
Visits an annotation value.

Params:
  • av – the value to visit
  • p – a visitor-specified parameter
Returns: a visitor-specified result
/**
     * 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 visit(av, null). 
Params:
  • av – the value to visit
Implementation Requirements:The default implementation is visit(av, null).
Returns: a visitor-specified result
/**
     * 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 boolean value in an annotation. 
Params:
  • b – the value being visited
  • p – a visitor-specified parameter
Returns:the result of the visit
/**
     * 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 byte value in an annotation. 
Params:
  • b – the value being visited
  • p – a visitor-specified parameter
Returns:the result of the visit
/**
     * 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 char value in an annotation. 
Params:
  • c – the value being visited
  • p – a visitor-specified parameter
Returns:the result of the visit
/**
     * 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 double value in an annotation. 
Params:
  • d – the value being visited
  • p – a visitor-specified parameter
Returns:the result of the visit
/**
     * 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 float value in an annotation. 
Params:
  • f – the value being visited
  • p – a visitor-specified parameter
Returns:the result of the visit
/**
     * 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 int value in an annotation. 
Params:
  • i – the value being visited
  • p – a visitor-specified parameter
Returns:the result of the visit
/**
     * 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 long value in an annotation. 
Params:
  • i – the value being visited
  • p – a visitor-specified parameter
Returns:the result of the visit
/**
     * 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 short value in an annotation. 
Params:
  • s – the value being visited
  • p – a visitor-specified parameter
Returns:the result of the visit
/**
     * 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.

Params:
  • s – the value being visited
  • p – a visitor-specified parameter
Returns:the result of the visit
/**
     * 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.

Params:
  • t – the value being visited
  • p – a visitor-specified parameter
Returns:the result of the visit
/**
     * 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 enum value in an annotation. 
Params:
  • c – the value being visited
  • p – a visitor-specified parameter
Returns:the result of the visit
/**
     * 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.

Params:
  • a – the value being visited
  • p – a visitor-specified parameter
Returns:the result of the visit
/**
     * 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.

Params:
  • vals – the value being visited
  • p – a visitor-specified parameter
Returns:the result of the visit
/**
     * 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<? extends AnnotationValue> 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.

Params:
  • av – the unknown value being visited
  • p – a visitor-specified parameter
Throws:
Returns:the result of the visit
/**
     * 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);
}