author | alanb |
Fri, 10 Feb 2017 09:06:10 +0000 | |
changeset 43767 | 9cff98a149cb |
parent 43260 | f5b52e571607 |
permissions | -rw-r--r-- |
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/* |
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* Copyright (c) 2005, 2017, Oracle and/or its affiliates. All rights reserved. |
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
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* |
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* This code is free software; you can redistribute it and/or modify it |
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* under the terms of the GNU General Public License version 2 only, as |
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* published by the Free Software Foundation. Oracle designates this |
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* particular file as subject to the "Classpath" exception as provided |
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* by Oracle in the LICENSE file that accompanied this code. |
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* |
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* This code is distributed in the hope that it will be useful, but WITHOUT |
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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* version 2 for more details (a copy is included in the LICENSE file that |
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* accompanied this code). |
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* |
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* You should have received a copy of the GNU General Public License version |
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* 2 along with this work; if not, write to the Free Software Foundation, |
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
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* |
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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* or visit www.oracle.com if you need additional information or have any |
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* questions. |
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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 <code>visit<i>Xyz</i></code> 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 were required to |
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* also be runnable on Java SE 7. Therefore, default methods |
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* were <em>not</em> used when extending {@code javax.lang.model.*} |
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* to cover Java SE 8 language features. However, default methods |
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* are 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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* @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 visit(e, null)}. |
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* |
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* @implSpec The default implementation is {@code visit(e, null)}. |
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* |
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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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default R visit(Element e) { |
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return visit(e, null); |
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} |
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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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* Visits a module element. |
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* |
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* @implSpec Visits a {@code ModuleElement} by calling {@code |
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* visitUnknown(e, p)}. |
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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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* @since 9 |
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* @spec JPMS |
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*/ |
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default R visitModule(ModuleElement e, P p) { |
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return visitUnknown(e, p); |
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} |
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} |