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  /*
   * This file is available under and governed by the GNU General Public
   * License version 2 only, as published by the Free Software Foundation.
   * However, the following notice accompanied the original version of this
   * file:
   *
   * Copyright (c) 2012, Stephen Colebourne & Michael Nascimento Santos
   *
   * All rights reserved.
   *
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   * modification, are permitted provided that the following conditions are met:
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   *    this list of conditions and the following disclaimer.
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  package java.time.chrono;
  
  import java.time.DateTimeException;
  
  /**
   * An era in the ISO calendar system.
   * <p>
   * The ISO-8601 standard does not define eras.
   * A definition has therefore been created with two eras - 'Current era' (CE) for
   * years on or after 0001-01-01 (ISO), and 'Before current era' (BCE) for years before that.
   *
   * <table summary="ISO years and eras" cellpadding="2" cellspacing="3" border="0" >
   * <thead>
   * <tr class="tableSubHeadingColor">
   * <th class="colFirst" align="left">year-of-era</th>
   * <th class="colFirst" align="left">era</th>
   * <th class="colLast" align="left">proleptic-year</th>
   * </tr>
   * </thead>
   * <tbody>
   * <tr class="rowColor">
   * <td>2</td><td>CE</td><td>2</td>
   * </tr>
   * <tr class="altColor">
   * <td>1</td><td>CE</td><td>1</td>
   * </tr>
   * <tr class="rowColor">
   * <td>1</td><td>BCE</td><td>0</td>
   * </tr>
   * <tr class="altColor">
   * <td>2</td><td>BCE</td><td>-1</td>
   * </tr>
   * </tbody>
   * </table>
   * <p>
   * <b>Do not use {@code ordinal()} to obtain the numeric representation of {@code IsoEra}.
   * Use {@code getValue()} instead.</b>
   *
   * @implSpec
   * This is an immutable and thread-safe enum.
   *
   * @since 1.8
   */
  public enum IsoEra implements Era {
  
      /**
       * The singleton instance for the era before the current one, 'Before Current Era',
       * which has the numeric value 0.
       */
      BCE,
      /**
       * The singleton instance for the current era, 'Current Era',
       * which has the numeric value 1.
       */
      CE;
  
      //-----------------------------------------------------------------------
      /**
       * Obtains an instance of {@code IsoEra} from an {@code int} value.
       * <p>
       * {@code IsoEra} is an enum representing the ISO eras of BCE/CE.
       * This factory allows the enum to be obtained from the {@code int} value.
       *
       * @param isoEra  the BCE/CE value to represent, from 0 (BCE) to 1 (CE)
       * @return the era singleton, not null
       * @throws DateTimeException if the value is invalid
       */
      public static IsoEra of(int isoEra) {
          switch (isoEra) {
              case 0:
                  return BCE;
              case 1:
                  return CE;
              default:
                  throw new DateTimeException("Invalid era: " + isoEra);
          }
      }
  
      //-----------------------------------------------------------------------
      /**
       * Gets the numeric era {@code int} value.
       * <p>
       * The era BCE has the value 0, while the era CE has the value 1.
       *
       * @return the era value, from 0 (BCE) to 1 (CE)
       */
      @Override
      public int getValue() {
          return ordinal();
      }
  
  }
  