src/java.base/share/classes/java/time/chrono/JapaneseEra.java

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 * 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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package java.time.chrono;

import static java.time.chrono.JapaneseDate.MEIJI_6_ISODATE;
import static java.time.temporal.ChronoField.ERA;

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import java.io.InvalidObjectException;
import java.io.ObjectInputStream;
import java.io.ObjectStreamException;
import java.io.Serializable;
import java.time.DateTimeException;
import java.time.LocalDate;
import java.time.format.DateTimeFormatterBuilder;
import java.time.format.TextStyle;
import java.time.temporal.ChronoField;
import java.time.temporal.TemporalField;
import java.time.temporal.UnsupportedTemporalTypeException;
import java.time.temporal.ValueRange;
import java.util.Arrays;
import java.util.Locale;
import java.util.Objects;

import sun.util.calendar.CalendarDate;

/**
 * An era in the Japanese Imperial calendar system.
 * <p>
 * The Japanese government defines the official name and start date of
 * each era. Eras are consecutive and their date ranges do not overlap,
 * so the end date of one era is always the day before the start date
 * of the next era.
 * <p>
 * The Java SE Platform supports all eras defined by the Japanese government,
 * beginning with the Meiji era. Each era is identified in the Platform by an
 * integer value and a name. The {@link #of(int)} and {@link #valueOf(String)}
 * methods may be used to obtain a singleton instance of {@code JapaneseEra}
 * for each era. The {@link #values()} method returns the singleton instances
 * of all supported eras.
 * <p>
 * For convenience, this class declares a number of public static final fields
 * that refer to singleton instances returned by the {@link #values()} method.
 *
 * @apiNote
 * The fields declared in this class may evolve over time, in line with the
 * results of the {@link #values()} method. However, there is not necessarily
 * a 1:1 correspondence between the fields and the singleton instances.
 *
 * @apiNote
 * The Japanese government may announce a new era and define its start
 * date but not its official name. In this scenario, the singleton instance
 * that represents the new era may return a name that is not stable until
 * the official name is defined. Developers should exercise caution when
 * relying on the name returned by any singleton instance that does not
 * correspond to a public static final field.
 *
 * @implSpec
 * This class is immutable and thread-safe.
 *
 * @since 1.8
 */
public final class JapaneseEra
        implements Era, Serializable {

    // The offset value to 0-based index from the era value.
    // i.e., getValue() + ERA_OFFSET == 0-based index
    static final int ERA_OFFSET = 2;

    static final sun.util.calendar.Era[] ERA_CONFIG;

    /**
     * The singleton instance for the 'Meiji' era (1868-01-01 - 1912-07-29)
     * which has the value -1.
     */
    public static final JapaneseEra MEIJI = new JapaneseEra(-1, LocalDate.of(1868, 1, 1));
    /**
     * The singleton instance for the 'Taisho' era (1912-07-30 - 1926-12-24)
     * which has the value 0.
     */
    public static final JapaneseEra TAISHO = new JapaneseEra(0, LocalDate.of(1912, 7, 30));
    /**
     * The singleton instance for the 'Showa' era (1926-12-25 - 1989-01-07)
     * which has the value 1.
     */
    public static final JapaneseEra SHOWA = new JapaneseEra(1, LocalDate.of(1926, 12, 25));
    /**
     * The singleton instance for the 'Heisei' era (1989-01-08 - 2019-04-30)
     * which has the value 2.
     */
    public static final JapaneseEra HEISEI = new JapaneseEra(2, LocalDate.of(1989, 1, 8));
    /**
     * The singleton instance for the 'Reiwa' era (2019-05-01 - )
     * which has the value 3. The end date of this era is not specified, unless
     * the Japanese Government defines it.
     *
     * @since 13
     */
    public static final JapaneseEra REIWA = new JapaneseEra(3, LocalDate.of(2019, 5, 1));

    // The number of predefined JapaneseEra constants.
    // There may be a supplemental era defined by the property.
    private static final int N_ERA_CONSTANTS = REIWA.getValue() + ERA_OFFSET;

    /**
     * Serialization version.
     */
    @java.io.Serial
    private static final long serialVersionUID = 1466499369062886794L;

    // array for the singleton JapaneseEra instances
    private static final JapaneseEra[] KNOWN_ERAS;

    static {
        ERA_CONFIG = JapaneseChronology.JCAL.getEras();

        KNOWN_ERAS = new JapaneseEra[ERA_CONFIG.length];
        KNOWN_ERAS[0] = MEIJI;
        KNOWN_ERAS[1] = TAISHO;
        KNOWN_ERAS[2] = SHOWA;
        KNOWN_ERAS[3] = HEISEI;
        KNOWN_ERAS[4] = REIWA;
        for (int i = N_ERA_CONSTANTS; i < ERA_CONFIG.length; i++) {
            CalendarDate date = ERA_CONFIG[i].getSinceDate();
            LocalDate isoDate = LocalDate.of(date.getYear(), date.getMonth(), date.getDayOfMonth());
            KNOWN_ERAS[i] = new JapaneseEra(i - ERA_OFFSET + 1, isoDate);
        }
    };

    /**
     * The era value.
     * @serial
     */
    private final transient int eraValue;

    // the first day of the era
    private final transient LocalDate since;

    /**
     * Creates an instance.
     *
     * @param eraValue  the era value, validated
     * @param since  the date representing the first date of the era, validated not null
     */
    private JapaneseEra(int eraValue, LocalDate since) {
        this.eraValue = eraValue;
        this.since = since;
    }

    //-----------------------------------------------------------------------
    /**
     * Returns the Sun private Era instance corresponding to this {@code JapaneseEra}.
     *
     * @return the Sun private Era instance for this {@code JapaneseEra}.
     */
    sun.util.calendar.Era getPrivateEra() {
        return ERA_CONFIG[ordinal(eraValue)];
    }

    //-----------------------------------------------------------------------
    /**
     * Obtains an instance of {@code JapaneseEra} from an {@code int} value.
     * <ul>
     * <li>The value {@code 1} is associated with the 'Showa' era, because
     * it contains 1970-01-01 (ISO calendar system).</li>
     * <li>The values {@code -1} and {@code 0} are associated with two earlier
     * eras, Meiji and Taisho, respectively.</li>
     * <li>A value greater than {@code 1} is associated with a later era,
     * beginning with Heisei ({@code 2}).</li>
     * </ul>
     * <p>
     * Every instance of {@code JapaneseEra} that is returned from the {@link #values()}
     * method has an int value (available via {@link Era#getValue()} which is
     * accepted by this method.
     *
     * @param japaneseEra  the era to represent
     * @return the {@code JapaneseEra} singleton, not null
     * @throws DateTimeException if the value is invalid
     */
    public static JapaneseEra of(int japaneseEra) {
        int i = ordinal(japaneseEra);
        if (i < 0 || i >= KNOWN_ERAS.length) {
            throw new DateTimeException("Invalid era: " + japaneseEra);
        }
        return KNOWN_ERAS[i];
    }

    /**
     * Returns the {@code JapaneseEra} with the name.
     * <p>
     * The string must match exactly the name of the era.
     * (Extraneous whitespace characters are not permitted.)
     * <p>
     * Valid era names are the names of eras returned from {@link #values()}.
     *
     * @param japaneseEra  the japaneseEra name; non-null
     * @return the {@code JapaneseEra} singleton, never null
     * @throws IllegalArgumentException if there is not JapaneseEra with the specified name
     */
    public static JapaneseEra valueOf(String japaneseEra) {
        Objects.requireNonNull(japaneseEra, "japaneseEra");
        for (JapaneseEra era : KNOWN_ERAS) {
            if (era.getName().equals(japaneseEra)) {
                return era;
            }
        }
        throw new IllegalArgumentException("japaneseEra is invalid");
    }

    /**
     * Returns an array of JapaneseEras. The array may contain eras defined
     * by the Japanese government beyond the known era singletons.
     *
     * <p>
     * This method may be used to iterate over the JapaneseEras as follows:
     * <pre>
     * for (JapaneseEra c : JapaneseEra.values())
     *     System.out.println(c);
     * </pre>
     *
     * @return an array of JapaneseEras
     */
    public static JapaneseEra[] values() {
        return Arrays.copyOf(KNOWN_ERAS, KNOWN_ERAS.length);
    }

    /**
     * {@inheritDoc}
     *
     * @param style {@inheritDoc}
     * @param locale {@inheritDoc}
     */
    @Override
    public String getDisplayName(TextStyle style, Locale locale) {
        // If this JapaneseEra is a supplemental one, obtain the name from
        // the era definition.
        if (getValue() > N_ERA_CONSTANTS - ERA_OFFSET) {
            Objects.requireNonNull(locale, "locale");
            return style.asNormal() == TextStyle.NARROW ? getAbbreviation() : getName();
        }

        return new DateTimeFormatterBuilder()
            .appendText(ERA, style)
            .toFormatter(locale)
            .withChronology(JapaneseChronology.INSTANCE)
            .format(this == MEIJI ? MEIJI_6_ISODATE : since);
    }

    //-----------------------------------------------------------------------
    /**
     * Obtains an instance of {@code JapaneseEra} from a date.
     *
     * @param date  the date, not null
     * @return the Era singleton, never null
     */
    static JapaneseEra from(LocalDate date) {
        if (date.isBefore(MEIJI_6_ISODATE)) {
            throw new DateTimeException("JapaneseDate before Meiji 6 are not supported");
        }
        for (int i = KNOWN_ERAS.length - 1; i > 0; i--) {
            JapaneseEra era = KNOWN_ERAS[i];
            if (date.compareTo(era.since) >= 0) {
                return era;
            }
        }
        return null;
    }

    static JapaneseEra toJapaneseEra(sun.util.calendar.Era privateEra) {
        for (int i = ERA_CONFIG.length - 1; i >= 0; i--) {
            if (ERA_CONFIG[i].equals(privateEra)) {
                return KNOWN_ERAS[i];
            }
        }
        return null;
    }

    static sun.util.calendar.Era privateEraFrom(LocalDate isoDate) {
        for (int i = KNOWN_ERAS.length - 1; i > 0; i--) {
            JapaneseEra era = KNOWN_ERAS[i];
            if (isoDate.compareTo(era.since) >= 0) {
                return ERA_CONFIG[i];
            }
        }
        return null;
    }

    /**
     * Returns the index into the arrays from the Era value.
     * the eraValue is a valid Era number, -1..2.
     *
     * @param eraValue  the era value to convert to the index
     * @return the index of the current Era
     */
    private static int ordinal(int eraValue) {
        return eraValue + ERA_OFFSET - 1;
    }

    //-----------------------------------------------------------------------
    /**
     * Gets the numeric era {@code int} value.
     * <p>
     * The {@link #SHOWA} era that contains 1970-01-01 (ISO calendar system) has the value 1.
     * Later eras are numbered from 2 ({@link #HEISEI}).
     * Earlier eras are numbered 0 ({@link #TAISHO}), -1 ({@link #MEIJI})).
     *
     * @return the era value
     */
    @Override
    public int getValue() {
        return eraValue;
    }

    //-----------------------------------------------------------------------
    /**
     * Gets the range of valid values for the specified field.
     * <p>
     * The range object expresses the minimum and maximum valid values for a field.
     * This era is used to enhance the accuracy of the returned range.
     * If it is not possible to return the range, because the field is not supported
     * or for some other reason, an exception is thrown.
     * <p>
     * If the field is a {@link ChronoField} then the query is implemented here.
     * The {@code ERA} field returns the range.
     * All other {@code ChronoField} instances will throw an {@code UnsupportedTemporalTypeException}.
     * <p>
     * If the field is not a {@code ChronoField}, then the result of this method
     * is obtained by invoking {@code TemporalField.rangeRefinedBy(TemporalAccessor)}
     * passing {@code this} as the argument.
     * Whether the range can be obtained is determined by the field.
     * <p>
     * The range of valid Japanese eras can change over time due to the nature
     * of the Japanese calendar system.
     *
     * @param field  the field to query the range for, not null
     * @return the range of valid values for the field, not null
     * @throws DateTimeException if the range for the field cannot be obtained
     * @throws UnsupportedTemporalTypeException if the unit is not supported
     */
    @Override  // override as super would return range from 0 to 1
    public ValueRange range(TemporalField field) {
        if (field == ERA) {
            return JapaneseChronology.INSTANCE.range(ERA);
        }
        return Era.super.range(field);
    }

    //-----------------------------------------------------------------------
    String getAbbreviation() {
        return ERA_CONFIG[ordinal(getValue())].getAbbreviation();
    }

    String getName() {
        return ERA_CONFIG[ordinal(getValue())].getName();
    }

    @Override
    public String toString() {
        return getName();
    }

    //-----------------------------------------------------------------------
    /**
     * Defend against malicious streams.
     *
     * @param s the stream to read
     * @throws InvalidObjectException always
     */
    @java.io.Serial
    private void readObject(ObjectInputStream s) throws InvalidObjectException {
        throw new InvalidObjectException("Deserialization via serialization delegate");
    }

    //-----------------------------------------------------------------------
    /**
     * Writes the object using a
     * <a href="{@docRoot}/serialized-form.html#java.time.chrono.Ser">dedicated serialized form</a>.
     * @serialData
     * <pre>
     *  out.writeByte(5);        // identifies a JapaneseEra
     *  out.writeInt(getValue());
     * </pre>
     *
     * @return the instance of {@code Ser}, not null
     */
    @java.io.Serial
    private Object writeReplace() {
        return new Ser(Ser.JAPANESE_ERA_TYPE, this);
    }

    void writeExternal(DataOutput out) throws IOException {
        out.writeByte(this.getValue());
    }

    static JapaneseEra readExternal(DataInput in) throws IOException {
        byte eraValue = in.readByte();
        return JapaneseEra.of(eraValue);
    }

}