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149 lines
4.7 KiB
149 lines
4.7 KiB
/*
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* Copyright (c) 2005, 2013, Oracle and/or its affiliates. All rights reserved.
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* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*/
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package javax.lang.model.element;
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import javax.lang.model.util.*;
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/**
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* A visitor of program elements, in the style of the visitor design
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* pattern. Classes implementing this interface are used to operate
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* on an element when the kind of element is unknown at compile time.
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* When a visitor is passed to an element's {@link Element#accept
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* accept} method, the <tt>visit<i>XYZ</i></tt> method most applicable
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* to that element is invoked.
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*
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* <p> Classes implementing this interface may or may not throw a
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* {@code NullPointerException} if the additional parameter {@code p}
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* is {@code null}; see documentation of the implementing class for
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* details.
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*
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* <p> <b>WARNING:</b> It is possible that methods will be added to
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* this interface to accommodate new, currently unknown, language
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* structures added to future versions of the Java™ programming
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* language. Therefore, visitor classes directly implementing this
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* interface may be source incompatible with future versions of the
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* platform. To avoid this source incompatibility, visitor
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* implementations are encouraged to instead extend the appropriate
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* abstract visitor class that implements this interface. However, an
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* API should generally use this visitor interface as the type for
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* parameters, return type, etc. rather than one of the abstract
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* classes.
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*
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* <p>Note that methods to accommodate new language constructs could
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* be added in a source <em>compatible</em> way if they were added as
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* <em>default methods</em>. However, default methods are only
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* available on Java SE 8 and higher releases and the {@code
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* javax.lang.model.*} packages bundled in Java SE 8 are required to
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* also be runnable on Java SE 7. Therefore, default methods
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* <em>cannot</em> be used when extending {@code javax.lang.model.*}
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* to cover Java SE 8 language features. However, default methods may
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* be used in subsequent revisions of the {@code javax.lang.model.*}
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* packages that are only required to run on Java SE 8 and higher
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* platform versions.
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*
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* @param <R> the return type of this visitor's methods. Use {@link
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* Void} for visitors that do not need to return results.
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* @param <P> the type of the additional parameter to this visitor's
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* methods. Use {@code Void} for visitors that do not need an
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* additional parameter.
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*
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* @author Joseph D. Darcy
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* @author Scott Seligman
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* @author Peter von der Ahé
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* @see AbstractElementVisitor6
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* @see AbstractElementVisitor7
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* @since 1.6
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*/
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public interface ElementVisitor<R, P> {
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/**
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* Visits an element.
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* @param e the element to visit
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* @param p a visitor-specified parameter
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* @return a visitor-specified result
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*/
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R visit(Element e, P p);
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/**
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* A convenience method equivalent to {@code v.visit(e, null)}.
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* @param e the element to visit
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* @return a visitor-specified result
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*/
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R visit(Element e);
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/**
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* Visits a package element.
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* @param e the element to visit
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* @param p a visitor-specified parameter
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* @return a visitor-specified result
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*/
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R visitPackage(PackageElement e, P p);
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/**
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* Visits a type element.
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* @param e the element to visit
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* @param p a visitor-specified parameter
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* @return a visitor-specified result
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*/
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R visitType(TypeElement e, P p);
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/**
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* Visits a variable element.
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* @param e the element to visit
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* @param p a visitor-specified parameter
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* @return a visitor-specified result
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*/
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R visitVariable(VariableElement e, P p);
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/**
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* Visits an executable element.
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* @param e the element to visit
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* @param p a visitor-specified parameter
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* @return a visitor-specified result
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*/
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R visitExecutable(ExecutableElement e, P p);
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/**
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* Visits a type parameter element.
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* @param e the element to visit
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* @param p a visitor-specified parameter
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* @return a visitor-specified result
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*/
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R visitTypeParameter(TypeParameterElement e, P p);
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/**
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* Visits an unknown kind of element.
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* This can occur if the language evolves and new kinds
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* of elements are added to the {@code Element} hierarchy.
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*
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* @param e the element to visit
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* @param p a visitor-specified parameter
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* @return a visitor-specified result
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* @throws UnknownElementException
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* a visitor implementation may optionally throw this exception
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*/
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R visitUnknown(Element e, P p);
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}
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