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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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 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions are met:

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 *  * Redistributions of source code must retain the above copyright notice,

 *    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 class="striped" style="text-align:left">

 * <caption style="display:none">ISO years and eras</caption>

 * <thead>

 * <tr>

 * <th scope="col">year-of-era</th>

 * <th scope="col">era</th>

 * <th scope="col">proleptic-year</th>

 * </tr>

 * </thead>

 * <tbody>

 * <tr>

 * <td>2</td><td>CE</td><th scope="row">2</th>

 * </tr>

 * <tr>

 * <td>1</td><td>CE</td><th scope="row">1</th>

 * </tr>

 * <tr>

 * <td>1</td><td>BCE</td><th scope="row">0</th>

 * </tr>

 * <tr>

 * <td>2</td><td>BCE</td><th scope="row">-1</th>

 * </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();

    }

}