openjdk/jdk/src/share/classes/java/time/chrono/IsoEra.java

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/*
 * This file is available under and governed by the GNU General Public
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 * However, the following notice accompanied the original version of this
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 * Copyright (c) 2012, Stephen Colebourne & Michael Nascimento Santos
 *
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package java.time.chrono;


import java.time.DateTimeException;
import java.time.LocalDate;

/**
 * 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 from 0001-01-01 (ISO) and 'Before current era' (BCE) for years before that.
 * <p>
 * <b>Do not use {@code ordinal()} to obtain the numeric representation of {@code IsoEra}.
 * Use {@code getValue()} instead.</b>
 *
 * <h3>Specification for implementors</h3>
 * This is an immutable and thread-safe enum.
 *
 * @since 1.8
 */
enum IsoEra implements Era {

    /**
     * The singleton instance for the era BCE, 'Before Current Era'.
     * The 'ISO' part of the name emphasizes that this differs from the BCE
     * era in the Gregorian calendar system.
     * This has the numeric value of {@code 0}.
     */
    BCE,
    /**
     * The singleton instance for the era CE, 'Current Era'.
     * The 'ISO' part of the name emphasizes that this differs from the CE
     * era in the Gregorian calendar system.
     * This has the numeric value of {@code 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 era  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 era) {
        switch (era) {
            case 0:
                return BCE;
            case 1:
                return CE;
            default:
                throw new DateTimeException("Invalid era: " + era);
        }
    }

    //-----------------------------------------------------------------------
    /**
     * 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();
    }

    @Override
    public IsoChronology getChronology() {
        return IsoChronology.INSTANCE;
    }

    // JDK8 default methods:
    //-----------------------------------------------------------------------
    @Override
    public LocalDate date(int year, int month, int day) {
        return getChronology().date(this, year, month, day);
    }

    @Override
    public LocalDate dateYearDay(int year, int dayOfYear) {
        return getChronology().dateYearDay(this, year, dayOfYear);
    }

}