| /* |
| * Copyright (c) 2005, 2017, Oracle and/or its affiliates. All rights reserved. |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
| * This code is free software; you can redistribute it and/or modify it |
| * under the terms of the GNU General Public License version 2 only, as |
| * published by the Free Software Foundation. Oracle designates this |
| * particular file as subject to the "Classpath" exception as provided |
| * by Oracle in the LICENSE file that accompanied this code. |
| * |
| * This code is distributed in the hope that it will be useful, but WITHOUT |
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.com if you need additional information or have any |
| * questions. |
| */ |
| |
| package javax.lang.model.element; |
| |
| import javax.lang.model.util.*; |
| |
| /** |
| * A visitor of program elements, in the style of the visitor design |
| * pattern. Classes implementing this interface are used to operate |
| * on an element when the kind of element is unknown at compile time. |
| * When a visitor is passed to an element's {@link Element#accept |
| * accept} method, the <code>visit<i>Xyz</i></code> method most applicable |
| * to that element 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™ 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. Use {@link |
| * Void} for visitors that do not need to return results. |
| * @param <P> the type of the additional parameter to this visitor's |
| * methods. Use {@code Void} for visitors that do not need an |
| * additional parameter. |
| * |
| * @author Joseph D. Darcy |
| * @author Scott Seligman |
| * @author Peter von der Ahé |
| * @since 1.6 |
| */ |
| public interface ElementVisitor<R, P> { |
| /** |
| * Visits an element. |
| * @param e the element to visit |
| * @param p a visitor-specified parameter |
| * @return a visitor-specified result |
| */ |
| R visit(Element e, P p); |
| |
| /** |
| * A convenience method equivalent to {@code visit(e, null)}. |
| * |
| * @implSpec The default implementation is {@code visit(e, null)}. |
| * |
| * @param e the element to visit |
| * @return a visitor-specified result |
| */ |
| default R visit(Element e) { |
| return visit(e, null); |
| } |
| |
| /** |
| * Visits a package element. |
| * @param e the element to visit |
| * @param p a visitor-specified parameter |
| * @return a visitor-specified result |
| */ |
| R visitPackage(PackageElement e, P p); |
| |
| /** |
| * Visits a type element. |
| * @param e the element to visit |
| * @param p a visitor-specified parameter |
| * @return a visitor-specified result |
| */ |
| R visitType(TypeElement e, P p); |
| |
| /** |
| * Visits a variable element. |
| * @param e the element to visit |
| * @param p a visitor-specified parameter |
| * @return a visitor-specified result |
| */ |
| R visitVariable(VariableElement e, P p); |
| |
| /** |
| * Visits an executable element. |
| * @param e the element to visit |
| * @param p a visitor-specified parameter |
| * @return a visitor-specified result |
| */ |
| R visitExecutable(ExecutableElement e, P p); |
| |
| /** |
| * Visits a type parameter element. |
| * @param e the element to visit |
| * @param p a visitor-specified parameter |
| * @return a visitor-specified result |
| */ |
| R visitTypeParameter(TypeParameterElement e, P p); |
| |
| /** |
| * Visits an unknown kind of element. |
| * This can occur if the language evolves and new kinds |
| * of elements are added to the {@code Element} hierarchy. |
| * |
| * @param e the element to visit |
| * @param p a visitor-specified parameter |
| * @return a visitor-specified result |
| * @throws UnknownElementException |
| * a visitor implementation may optionally throw this exception |
| */ |
| R visitUnknown(Element e, P p); |
| |
| /** |
| * Visits a module element. |
| * |
| * @implSpec The default implementation visits a {@code |
| * ModuleElement} by calling {@code visitUnknown(e, p)}. |
| * |
| * @param e the element to visit |
| * @param p a visitor-specified parameter |
| * @return a visitor-specified result |
| * @since 9 |
| * @spec JPMS |
| */ |
| default R visitModule(ModuleElement e, P p) { |
| return visitUnknown(e, p); |
| } |
| } |