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   * Copyright (c) 2005, 2020, 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
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   */
  
  package jdkx.lang.model.util;
  
  import jdkx.annotation.processing.SupportedSourceVersion;
  import jdkx.lang.model.SourceVersion;
  import jdkx.lang.model.element.*;
  import static jdkx.lang.model.SourceVersion.*;
  
  
  /**
   * A skeletal visitor of program elements with default behavior
   * appropriate for the {@link SourceVersion#RELEASE_6 RELEASE_6}
   * source version.
   *
   * @apiNote
   * <p id=note_for_subclasses><strong>WARNING:</strong> The {@code
   * ElementVisitor} interface implemented by this class may have
   * methods added to it in the future to accommodate new, currently
   * unknown, language structures added to future versions of the
   * Java programming language.  Therefore, methods whose names
   * begin with {@code "visit"} may be added to this class in the
   * future; to avoid incompatibilities, classes and subclasses which
   * extend this class should not declare any instance methods with
   * names beginning with {@code "visit"}.</p>
   *
   * <p>When such a new visit method is added, the default
   * implementation in this class will be to directly or indirectly call
   * the {@link #visitUnknown visitUnknown} method.  A new abstract
   * element visitor class will also be introduced to correspond to the
   * new language level; this visitor will have different default
   * behavior for the visit method in question.  When a new visitor is
   * introduced, portions of this visitor class may be deprecated,
   * including its constructors.
   *
   * @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 Ah&eacute;
   *
   * @see AbstractElementVisitor7
   * @see AbstractElementVisitor8
   * @see AbstractElementVisitor9
   * @see AbstractElementVisitor14
   * @since 1.6
   */
  @SupportedSourceVersion(RELEASE_6)
  public abstract class AbstractElementVisitor6<R, P> implements ElementVisitor<R, P> {
      /**
       * Constructor for concrete subclasses to call.
       * @deprecated Release 6 is obsolete; update to a visitor for a newer
       * release level.
       */
      @Deprecated(since="9")
      protected AbstractElementVisitor6(){}
  
      /**
       * Visits any program element as if by passing itself to that
       * element's {@link Element#accept accept} method.  The invocation
       * {@code v.visit(elem, p)} is equivalent to {@code elem.accept(v,
       * p)}.
       *
       * @param e  the element to visit
       * @param p  a visitor-specified parameter
       * @return a visitor-specified result
       */
      public final R visit(Element e, P p) {
          return e.accept(this, p);
      }
  
      /**
       * Visits any program element as if by passing itself to that
       * element's {@link Element#accept accept} method and passing
       * {@code null} for the additional parameter.  The invocation
       * {@code v.visit(elem)} is equivalent to {@code elem.accept(v,
       * null)}.
       *
       * @param e  the element to visit
       * @return a visitor-specified result
       */
      public final R visit(Element e) {
          return e.accept(this, null);
      }
  
      /**
       * {@inheritDoc}
       *
       * @implSpec The default implementation of this method in
       * {@code AbstractElementVisitor6} will always throw
       * {@code new UnknownElementException(e, p)}.
       * This behavior is not required of a subclass.
       *
       * @param e {@inheritDoc}
       * @param p {@inheritDoc}
       * @return  {@inheritDoc}
       * @throws UnknownElementException
       *          a visitor implementation may optionally throw this exception
       */
      @Override
      public R visitUnknown(Element e, P p) {
          throw new UnknownElementException(e, p);
      }
  
      /**
       * {@inheritDoc}
       *
       * @implSpec Visits a {@code ModuleElement} by calling {@code
       * visitUnknown}.
       *
       * @param e  {@inheritDoc}
       * @param p  {@inheritDoc}
       * @return   {@inheritDoc}
       *
       * @since 9
       */
      @Override
      public R visitModule(ModuleElement e, P p) {
          // Use implementation from interface default method
          return ElementVisitor.super.visitModule(e, p);
      }
  
      /**
       * {@inheritDoc}
       *
       * @implSpec Visits a {@code RecordComponentElement} by calling {@code
       * visitUnknown}.
       *
       * @param e  {@inheritDoc}
       * @param p  {@inheritDoc}
       * @return   {@inheritDoc}
       *
       * @since 14
       */
      @SuppressWarnings("preview")
      @Override
      public R visitRecordComponent(RecordComponentElement e, P p) {
          // Use implementation from interface default method
          return ElementVisitor.super.visitRecordComponent(e, p);
      }
  }
  