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   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   * 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.lang.model.element.*;
  import jdkx.annotation.processing.SupportedSourceVersion;
  import jdkx.lang.model.SourceVersion;
  import static jdkx.lang.model.SourceVersion.*;
  
  
  /**
   * A simple visitor of program elements with default behavior
   * appropriate for the {@link SourceVersion#RELEASE_6 RELEASE_6}
   * source version.
   *
   * Visit methods corresponding to {@code RELEASE_6} language
   * constructs call {@link #defaultAction defaultAction}, passing their
   * arguments to {@code defaultAction}'s corresponding parameters.
   *
   * For constructs introduced in {@code RELEASE_7} and later, {@code
   * visitUnknown} is called instead.
   *
   *
   * @apiNote
   * Methods in this class may be overridden subject to their general
   * contract.
   *
   * <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 simple
   * 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 {@code 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 SimpleElementVisitor7
   * @see SimpleElementVisitor8
   * @see SimpleElementVisitor9
   * @see SimpleElementVisitor14
   * @since 1.6
   */
  @SupportedSourceVersion(RELEASE_6)
  public class SimpleElementVisitor6<R, P> extends AbstractElementVisitor6<R, P> {
      /**
       * Default value to be returned; {@link #defaultAction
       * defaultAction} returns this value unless the method is
       * overridden.
       */
      protected final R DEFAULT_VALUE;
  
      /**
       * Constructor for concrete subclasses; uses {@code null} for the
       * default value.
       * @deprecated Release 6 is obsolete; update to a visitor for a newer
       * release level.
       */
      @Deprecated(since="9")
      protected SimpleElementVisitor6(){
          DEFAULT_VALUE = null;
      }
  
      /**
       * Constructor for concrete subclasses; uses the argument for the
       * default value.
       *
       * @param defaultValue the value to assign to {@link #DEFAULT_VALUE}
       * @deprecated Release 6 is obsolete; update to a visitor for a newer
       * release level.
       */
      @Deprecated(since="9")
      protected SimpleElementVisitor6(R defaultValue){
          DEFAULT_VALUE = defaultValue;
      }
      /**
       * The default action for visit methods.
       *
       * @implSpec The implementation in this class just returns {@link
       * #DEFAULT_VALUE}; subclasses will commonly override this method.
       *
       * @param e the element to process
       * @param p a visitor-specified parameter
       * @return {@code DEFAULT_VALUE} unless overridden
       */
      protected R defaultAction(Element e, P p) {
          return DEFAULT_VALUE;
      }
  
      /**
       * {@inheritDoc}
       *
       * @implSpec This implementation calls {@code defaultAction}.
       *
       * @param e {@inheritDoc}
       * @param p {@inheritDoc}
       * @return  {@inheritDoc}
       */
      public R visitPackage(PackageElement e, P p) {
          return defaultAction(e, p);
      }
  
      /**
       * {@inheritDoc}
       *
       * @implSpec This implementation calls {@code defaultAction}.
       *
       * @param e {@inheritDoc}
       * @param p {@inheritDoc}
       * @return  {@inheritDoc}
       */
      public R visitType(TypeElement e, P p) {
          return defaultAction(e, p);
      }
  
      /**
       * {@inheritDoc}
       *
       * @implSpec This implementation calls {@code defaultAction}, unless the
       * element is a {@code RESOURCE_VARIABLE} in which case {@code
       * visitUnknown} is called.
       *
       * @param e {@inheritDoc}
       * @param p {@inheritDoc}
       * @return  {@inheritDoc}
       */
      public R visitVariable(VariableElement e, P p) {
          if (e.getKind() != ElementKind.RESOURCE_VARIABLE)
              return defaultAction(e, p);
          else
              return visitUnknown(e, p);
      }
  
      /**
       * {@inheritDoc}
       *
       * @implSpec This implementation calls {@code defaultAction}.
       *
       * @param e {@inheritDoc}
       * @param p {@inheritDoc}
       * @return  {@inheritDoc}
       */
      public R visitExecutable(ExecutableElement e, P p) {
          return defaultAction(e, p);
      }
  
      /**
       * {@inheritDoc}
       *
       * @implSpec This implementation calls {@code defaultAction}.
       *
       * @param e {@inheritDoc}
       * @param p {@inheritDoc}
       * @return  {@inheritDoc}
       */
      public R visitTypeParameter(TypeParameterElement e, P p) {
          return defaultAction(e, p);
      }
  }
  