bp/chrono/ChronoLocalDate.java

/*
 * Copyright (c) 2007-present, Stephen Colebourne & Michael Nascimento Santos
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *  * Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 *
 *  * Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 *  * Neither the name of JSR-310 nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package org.threeten.bp.chrono;

import static org.threeten.bp.temporal.ChronoField.DAY_OF_MONTH;
import static org.threeten.bp.temporal.ChronoField.EPOCH_DAY;
import static org.threeten.bp.temporal.ChronoField.ERA;
import static org.threeten.bp.temporal.ChronoField.MONTH_OF_YEAR;
import static org.threeten.bp.temporal.ChronoField.YEAR;
import static org.threeten.bp.temporal.ChronoField.YEAR_OF_ERA;

import java.util.Comparator;

import org.threeten.bp.DateTimeException;
import org.threeten.bp.LocalDate;
import org.threeten.bp.LocalTime;
import org.threeten.bp.format.DateTimeFormatter;
import org.threeten.bp.jdk8.DefaultInterfaceTemporal;
import org.threeten.bp.jdk8.Jdk8Methods;
import org.threeten.bp.temporal.ChronoField;
import org.threeten.bp.temporal.ChronoUnit;
import org.threeten.bp.temporal.Temporal;
import org.threeten.bp.temporal.TemporalAccessor;
import org.threeten.bp.temporal.TemporalAdjuster;
import org.threeten.bp.temporal.TemporalAmount;
import org.threeten.bp.temporal.TemporalField;
import org.threeten.bp.temporal.TemporalQueries;
import org.threeten.bp.temporal.TemporalQuery;
import org.threeten.bp.temporal.TemporalUnit;

/**
 * A date without time-of-day or time-zone in an arbitrary chronology, intended
 * for advanced globalization use cases.
 * <p>
 * <b>Most applications should declare method signatures, fields and variables
 * as {@link LocalDate}, not this interface.</b>
 * <p>
 * A {@code ChronoLocalDate} is the abstract representation of a date where the
 * {@code Chronology chronology}, or calendar system, is pluggable.
 * The date is defined in terms of fields expressed by {@link TemporalField},
 * where most common implementations are defined in {@link ChronoField}.
 * The chronology defines how the calendar system operates and the meaning of
 * the standard fields.
 *
 * <h4>When to use this interface</h4>
 * The design of the API encourages the use of {@code LocalDate} rather than this
 * interface, even in the case where the application needs to deal with multiple
 * calendar systems. The rationale for this is explored in the following documentation.
 * <p>
 * The primary use case where this interface should be used is where the generic
 * type parameter {@code <C>} is fully defined as a specific chronology.
 * In that case, the assumptions of that chronology are known at development
 * time and specified in the code.
 * <p>
 * When the chronology is defined in the generic type parameter as ? or otherwise
 * unknown at development time, the rest of the discussion below applies.
 * <p>
 * To emphasize the point, declaring a method signature, field or variable as this
 * interface type can initially seem like the sensible way to globalize an application,
 * however it is usually the wrong approach.
 * As such, it should be considered an application-wide architectural decision to choose
 * to use this interface as opposed to {@code LocalDate}.
 *
 * <h4>Architectural issues to consider</h4>
 * These are some of the points that must be considered before using this interface
 * throughout an application.
 * <p>
 * 1) Applications using this interface, as opposed to using just {@code LocalDate},
 * face a significantly higher probability of bugs. This is because the calendar system
 * in use is not known at development time. A key cause of bugs is where the developer
 * applies assumptions from their day-to-day knowledge of the ISO calendar system
 * to code that is intended to deal with any arbitrary calendar system.
 * The section below outlines how those assumptions can cause problems
 * The primary mechanism for reducing this increased risk of bugs is a strong code review process.
 * This should also be considered a extra cost in maintenance for the lifetime of the code.
 * <p>
 * 2) This interface does not enforce immutability of implementations.
 * While the implementation notes indicate that all implementations must be immutable
 * there is nothing in the code or type system to enforce this. Any method declared
 * to accept a {@code ChronoLocalDate} could therefore be passed a poorly or
 * maliciously written mutable implementation.
 * <p>
 * 3) Applications using this interface  must consider the impact of eras.
 * {@code LocalDate} shields users from the concept of eras, by ensuring that {@code getYear()}
 * returns the proleptic year. That decision ensures that developers can think of
 * {@code LocalDate} instances as consisting of three fields - year, month-of-year and day-of-month.
 * By contrast, users of this interface must think of dates as consisting of four fields -
 * era, year-of-era, month-of-year and day-of-month. The extra era field is frequently
 * forgotten, yet it is of vital importance to dates in an arbitrary calendar system.
 * For example, in the Japanese calendar system, the era represents the reign of an Emperor.
 * Whenever one reign ends and another starts, the year-of-era is reset to one.
 * <p>
 * 4) The only agreed international standard for passing a date between two systems
 * is the ISO-8601 standard which requires the ISO calendar system. Using this interface
 * throughout the application will inevitably lead to the requirement to pass the date
 * across a network or component boundary, requiring an application specific protocol or format.
 * <p>
 * 5) Long term persistence, such as a database, will almost always only accept dates in the
 * ISO-8601 calendar system (or the related Julian-Gregorian). Passing around dates in other
 * calendar systems increases the complications of interacting with persistence.
 * <p>
 * 6) Most of the time, passing a {@code ChronoLocalDate} throughout an application
 * is unnecessary, as discussed in the last section below.
 *
 * <h4>False assumptions causing bugs in multi-calendar system code</h4>
 * As indicated above, there are many issues to consider when try to use and manipulate a
 * date in an arbitrary calendar system. These are some of the key issues.
 * <p>
 * Code that queries the day-of-month and assumes that the value will never be more than
 * 31 is invalid. Some calendar systems have more than 31 days in some months.
 * <p>
 * Code that adds 12 months to a date and assumes that a year has been added is invalid.
 * Some calendar systems have a different number of months, such as 13 in the Coptic or Ethiopic.
 * <p>
 * Code that adds one month to a date and assumes that the month-of-year value will increase
 * by one or wrap to the next year is invalid. Some calendar systems have a variable number
 * of months in a year, such as the Hebrew.
 * <p>
 * Code that adds one month, then adds a second one month and assumes that the day-of-month
 * will remain close to its original value is invalid. Some calendar systems have a large difference
 * between the length of the longest month and the length of the shortest month.
 * For example, the Coptic or Ethiopic have 12 months of 30 days and 1 month of 5 days.
 * <p>
 * Code that adds seven days and assumes that a week has been added is invalid.
 * Some calendar systems have weeks of other than seven days, such as the French Revolutionary.
 * <p>
 * Code that assumes that because the year of {@code date1} is greater than the year of {@code date2}
 * then {@code date1} is after {@code date2} is invalid. This is invalid for all calendar systems
 * when referring to the year-of-era, and especially untrue of the Japanese calendar system
 * where the year-of-era restarts with the reign of every new Emperor.
 * <p>
 * Code that treats month-of-year one and day-of-month one as the start of the year is invalid.
 * Not all calendar systems start the year when the month value is one.
 * <p>
 * In general, manipulating a date, and even querying a date, is wide open to bugs when the
 * calendar system is unknown at development time. This is why it is essential that code using
 * this interface is subjected to additional code reviews. It is also why an architectural
 * decision to avoid this interface type is usually the correct one.
 *
 * <h4>Using LocalDate instead</h4>
 * The primary alternative to using this interface throughout your application is as follows.
 * <p><ul>
 * <li>Declare all method signatures referring to dates in terms of {@code LocalDate}.
 * <li>Either store the chronology (calendar system) in the user profile or lookup
 *  the chronology from the user locale
 * <li>Convert the ISO {@code LocalDate} to and from the user's preferred calendar system during
 *  printing and parsing
 * </ul><p>
 * This approach treats the problem of globalized calendar systems as a localization issue
 * and confines it to the UI layer. This approach is in keeping with other localization
 * issues in the java platform.
 * <p>
 * As discussed above, performing calculations on a date where the rules of the calendar system
 * are pluggable requires skill and is not recommended.
 * Fortunately, the need to perform calculations on a date in an arbitrary calendar system
 * is extremely rare. For example, it is highly unlikely that the business rules of a library
 * book rental scheme will allow rentals to be for one month, where meaning of the month
 * is dependent on the user's preferred calendar system.
 * <p>
 * A key use case for calculations on a date in an arbitrary calendar system is producing
 * a month-by-month calendar for display and user interaction. Again, this is a UI issue,
 * and use of this interface solely within a few methods of the UI layer may be justified.
 * <p>
 * In any other part of the system, where a date must be manipulated in a calendar system
 * other than ISO, the use case will generally specify the calendar system to use.
 * For example, an application may need to calculate the next Islamic or Hebrew holiday
 * which may require manipulating the date.
 * This kind of use case can be handled as follows:
 * <p><ul>
 * <li>start from the ISO {@code LocalDate} being passed to the method
 * <li>convert the date to the alternate calendar system, which for this use case is known
 *  rather than arbitrary
 * <li>perform the calculation
 * <li>convert back to {@code LocalDate}
 * </ul><p>
 * Developers writing low-level frameworks or libraries should also avoid this interface.
 * Instead, one of the two general purpose access interfaces should be used.
 * Use {@link TemporalAccessor} if read-only access is required, or use {@link Temporal}
 * if read-write access is required.
 *
 * <h3>Specification for implementors</h3>
 * This interface must be implemented with care to ensure other classes operate correctly.
 * All implementations that can be instantiated must be final, immutable and thread-safe.
 * Subclasses should be Serializable wherever possible.
 * <p>
 * Additional calendar systems may be added to the system.
 * See {@link Chronology} for more details.
 * <p>
 * In JDK 8, this is an interface with default methods.
 * Since there are no default methods in JDK 7, an abstract class is used.
 */
public abstract class ChronoLocalDate
        extends DefaultInterfaceTemporal
        implements Temporal, TemporalAdjuster, Comparable<ChronoLocalDate> {

    /**
     * Gets a comparator that compares {@code ChronoLocalDate} in
     * time-line order ignoring the chronology.
     * <p>
     * This comparator differs from the comparison in {@link #compareTo} in that it
     * only compares the underlying date and not the chronology.
     * This allows dates in different calendar systems to be compared based
     * on the position of the date on the local time-line.
     * The underlying comparison is equivalent to comparing the epoch-day.
     *
     * @return a comparator that compares in time-line order ignoring the chronology
     * @see #isAfter
     * @see #isBefore
     * @see #isEqual
     */
    public static Comparator<ChronoLocalDate> timeLineOrder() {
        return DATE_COMPARATOR;
    }
    private static final Comparator<ChronoLocalDate> DATE_COMPARATOR =
            new Comparator<ChronoLocalDate>() {
        @Override
        public int compare(ChronoLocalDate date1, ChronoLocalDate date2) {
            return Jdk8Methods.compareLongs(date1.toEpochDay(), date2.toEpochDay());
        }
    };

    //-----------------------------------------------------------------------
    /**
     * Obtains an instance of {@code ChronoLocalDate} from a temporal object.
     * <p>
     * This obtains a local date based on the specified temporal.
     * A {@code TemporalAccessor} represents an arbitrary set of date and time information,
     * which this factory converts to an instance of {@code ChronoLocalDate}.
     * <p>
     * The conversion extracts and combines the chronology and the date
     * from the temporal object. The behavior is equivalent to using
     * {@link Chronology#date(TemporalAccessor)} with the extracted chronology.
     * Implementations are permitted to perform optimizations such as accessing
     * those fields that are equivalent to the relevant objects.
     * <p>
     * This method matches the signature of the functional interface {@link TemporalQuery}
     * allowing it to be used as a query via method reference, {@code ChronoLocalDate::from}.
     *
     * @param temporal  the temporal object to convert, not null
     * @return the date, not null
     * @throws DateTimeException if unable to convert to a {@code ChronoLocalDate}
     * @see Chronology#date(TemporalAccessor)
     */
    public static ChronoLocalDate from(TemporalAccessor temporal) {
        Jdk8Methods.requireNonNull(temporal, "temporal");
        if (temporal instanceof ChronoLocalDate) {
            return (ChronoLocalDate) temporal;
        }
        Chronology chrono = temporal.query(TemporalQueries.chronology());
        if (chrono == null) {
            throw new DateTimeException("No Chronology found to create ChronoLocalDate: " + temporal.getClass());
        }
        return chrono.date(temporal);
    }

    //-----------------------------------------------------------------------
    /**
     * Gets the chronology of this date.
     * <p>
     * The {@code Chronology} represents the calendar system in use.
     * The era and other fields in {@link ChronoField} are defined by the chronology.
     *
     * @return the chronology, not null
     */
    public abstract Chronology getChronology();

    /**
     * Gets the era, as defined by the chronology.
     * <p>
     * The era is, conceptually, the largest division of the time-line.
     * Most calendar systems have a single epoch dividing the time-line into two eras.
     * However, some have multiple eras, such as one for the reign of each leader.
     * The exact meaning is determined by the {@code Chronology}.
     * <p>
     * All correctly implemented {@code Era} classes are singletons, thus it
     * is valid code to write {@code date.getEra() == SomeEra.NAME)}.
     *
     * @return the chronology specific era constant applicable at this date, not null
     */
    public Era getEra() {
        return getChronology().eraOf(get(ERA));
    }

    //-----------------------------------------------------------------------
    /**
     * Checks if the year is a leap year, as defined by the calendar system.
     * <p>
     * A leap-year is a year of a longer length than normal.
     * The exact meaning is determined by the chronology with the constraint that
     * a leap-year must imply a year-length longer than a non leap-year.
     * <p>
     * The default implementation uses {@link Chronology#isLeapYear(long)}.
     *
     * @return true if this date is in a leap year, false otherwise
     */
    public boolean isLeapYear() {
        return getChronology().isLeapYear(getLong(YEAR));
    }

    /**
     * Returns the length of the month represented by this date, as defined by the calendar system.
     * <p>
     * This returns the length of the month in days.
     *
     * @return the length of the month in days
     */
    public abstract int lengthOfMonth();

    /**
     * Returns the length of the year represented by this date, as defined by the calendar system.
     * <p>
     * This returns the length of the year in days.
     * <p>
     * The default implementation uses {@link #isLeapYear()} and returns 365 or 366.
     *
     * @return the length of the year in days
     */
    public int lengthOfYear() {
        return (isLeapYear() ? 366 : 365);
    }

    @Override
    public boolean isSupported(TemporalField field) {
        if (field instanceof ChronoField) {
            return field.isDateBased();
        }
        return field != null && field.isSupportedBy(this);
    }

    @Override
    public boolean isSupported(TemporalUnit unit) {
        if (unit instanceof ChronoUnit) {
            return unit.isDateBased();
        }
        return unit != null && unit.isSupportedBy(this);
    }

    //-------------------------------------------------------------------------
    // override for covariant return type
    @Override
    public ChronoLocalDate with(TemporalAdjuster adjuster) {
        return getChronology().ensureChronoLocalDate(super.with(adjuster));
    }

    @Override
    public abstract ChronoLocalDate with(TemporalField field, long newValue);

    @Override
    public ChronoLocalDate plus(TemporalAmount amount) {
        return getChronology().ensureChronoLocalDate(super.plus(amount));
    }

    @Override
    public abstract ChronoLocalDate plus(long amountToAdd, TemporalUnit unit);

    @Override
    public ChronoLocalDate minus(TemporalAmount amount) {
        return getChronology().ensureChronoLocalDate(super.minus(amount));
    }

    @Override
    public ChronoLocalDate minus(long amountToSubtract, TemporalUnit unit) {
        return getChronology().ensureChronoLocalDate(super.minus(amountToSubtract, unit));
    }

    //-----------------------------------------------------------------------
    @SuppressWarnings("unchecked")
    @Override
    public <R> R query(TemporalQuery<R> query) {
        if (query == TemporalQueries.chronology()) {
            return (R) getChronology();
        } else if (query == TemporalQueries.precision()) {
            return (R) ChronoUnit.DAYS;
        } else if (query == TemporalQueries.localDate()) {
            return (R) LocalDate.ofEpochDay(toEpochDay());
        } else if (query == TemporalQueries.localTime() || query == TemporalQueries.zone() ||
                query == TemporalQueries.zoneId() || query == TemporalQueries.offset()) {
            return null;
        }
        return super.query(query);
    }

    @Override
    public Temporal adjustInto(Temporal temporal) {
        return temporal.with(EPOCH_DAY, toEpochDay());
    }

    //-----------------------------------------------------------------------
    /**
     * Calculates the period between this date and another date as a {@code ChronoPeriod}.
     * <p>
     * This calculates the period between two dates. All supplied chronologies
     * calculate the period using years, months and days, however the
     * {@code ChronoPeriod} API allows the period to be represented using other units.
     * <p>
     * The start and end points are {@code this} and the specified date.
     * The result will be negative if the end is before the start.
     * The negative sign will be the same in each of year, month and day.
     * <p>
     * The calculation is performed using the chronology of this date.
     * If necessary, the input date will be converted to match.
     * <p>
     * This instance is immutable and unaffected by this method call.
     *
     * @param endDateExclusive  the end date, exclusive, which may be in any chronology, not null
     * @return the period between this date and the end date, not null
     * @throws DateTimeException if the period cannot be calculated
     * @throws ArithmeticException if numeric overflow occurs
     */
    public abstract ChronoPeriod until(ChronoLocalDate endDateExclusive);

    /**
     * Formats this date using the specified formatter.
     * <p>
     * This date will be passed to the formatter to produce a string.
     * <p>
     * The default implementation must behave as follows:
     * <pre>
     *  return formatter.format(this);
     * </pre>
     *
     * @param formatter  the formatter to use, not null
     * @return the formatted date string, not null
     * @throws DateTimeException if an error occurs during printing
     */
    public String format(DateTimeFormatter formatter) {
        Jdk8Methods.requireNonNull(formatter, "formatter");
        return formatter.format(this);
    }

    //-----------------------------------------------------------------------
    /**
     * Combines this date with a time to create a {@code ChronoLocalDateTime}.
     * <p>
     * This returns a {@code ChronoLocalDateTime} formed from this date at the specified time.
     * All possible combinations of date and time are valid.
     *
     * @param localTime  the local time to use, not null
     * @return the local date-time formed from this date and the specified time, not null
     */
    public ChronoLocalDateTime<?> atTime(LocalTime localTime) {
        return ChronoLocalDateTimeImpl.of(this, localTime);
    }

    //-----------------------------------------------------------------------
    /**
     * Converts this date to the Epoch Day.
     * <p>
     * The {@link ChronoField#EPOCH_DAY Epoch Day count} is a simple
     * incrementing count of days where day 0 is 1970-01-01 (ISO).
     * This definition is the same for all chronologies, enabling conversion.
     *
     * @return the Epoch Day equivalent to this date
     */
    public long toEpochDay() {
        return getLong(EPOCH_DAY);
    }

    //-----------------------------------------------------------------------
    /**
     * Compares this date to another date, including the chronology.
     * <p>
     * The comparison is based first on the underlying time-line date, then
     * on the chronology.
     * It is "consistent with equals", as defined by {@link Comparable}.
     * <p>
     * For example, the following is the comparator order:
     * <ol>
     * <li>{@code 2012-12-03 (ISO)}</li>
     * <li>{@code 2012-12-04 (ISO)}</li>
     * <li>{@code 2555-12-04 (ThaiBuddhist)}</li>
     * <li>{@code 2012-12-05 (ISO)}</li>
     * </ol>
     * Values #2 and #3 represent the same date on the time-line.
     * When two values represent the same date, the chronology ID is compared to distinguish them.
     * This step is needed to make the ordering "consistent with equals".
     * <p>
     * If all the date objects being compared are in the same chronology, then the
     * additional chronology stage is not required and only the local date is used.
     * To compare the dates of two {@code TemporalAccessor} instances, including dates
     * in two different chronologies, use {@link ChronoField#EPOCH_DAY} as a comparator.
     *
     * @param other  the other date to compare to, not null
     * @return the comparator value, negative if less, positive if greater
     */
    @Override
    public int compareTo(ChronoLocalDate other) {
        int cmp = Jdk8Methods.compareLongs(toEpochDay(), other.toEpochDay());
        if (cmp == 0) {
            cmp = getChronology().compareTo(other.getChronology());
        }
        return cmp;
    }

    //-----------------------------------------------------------------------
    /**
     * Checks if this date is after the specified date ignoring the chronology.
     * <p>
     * This method differs from the comparison in {@link #compareTo} in that it
     * only compares the underlying date and not the chronology.
     * This allows dates in different calendar systems to be compared based
     * on the time-line position.
     * This is equivalent to using {@code date1.toEpochDay() &gt; date2.toEpochDay()}.
     *
     * @param other  the other date to compare to, not null
     * @return true if this is after the specified date
     */
    public boolean isAfter(ChronoLocalDate other) {
        return this.toEpochDay() > other.toEpochDay();
    }

    /**
     * Checks if this date is before the specified date ignoring the chronology.
     * <p>
     * This method differs from the comparison in {@link #compareTo} in that it
     * only compares the underlying date and not the chronology.
     * This allows dates in different calendar systems to be compared based
     * on the time-line position.
     * This is equivalent to using {@code date1.toEpochDay() &lt; date2.toEpochDay()}.
     *
     * @param other  the other date to compare to, not null
     * @return true if this is before the specified date
     */
    public boolean isBefore(ChronoLocalDate other) {
        return this.toEpochDay() < other.toEpochDay();
    }

    /**
     * Checks if this date is equal to the specified date ignoring the chronology.
     * <p>
     * This method differs from the comparison in {@link #compareTo} in that it
     * only compares the underlying date and not the chronology.
     * This allows dates in different calendar systems to be compared based
     * on the time-line position.
     * This is equivalent to using {@code date1.toEpochDay() == date2.toEpochDay()}.
     *
     * @param other  the other date to compare to, not null
     * @return true if the underlying date is equal to the specified date
     */
    public boolean isEqual(ChronoLocalDate other) {
        return this.toEpochDay() == other.toEpochDay();
    }

    //-----------------------------------------------------------------------
    /**
     * Checks if this date is equal to another date, including the chronology.
     * <p>
     * Compares this date with another ensuring that the date and chronology are the same.
     * <p>
     * To compare the dates of two {@code TemporalAccessor} instances, including dates
     * in two different chronologies, use {@link ChronoField#EPOCH_DAY} as a comparator.
     *
     * @param obj  the object to check, null returns false
     * @return true if this is equal to the other date
     */
    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj instanceof ChronoLocalDate) {
            return compareTo((ChronoLocalDate) obj) == 0;
        }
        return false;
    }

    /**
     * A hash code for this date.
     *
     * @return a suitable hash code
     */
    @Override
    public int hashCode() {
        long epDay = toEpochDay();
        return getChronology().hashCode() ^ ((int) (epDay ^ (epDay >>> 32)));
    }

    //-----------------------------------------------------------------------
    /**
     * Outputs this date as a {@code String}.
     * <p>
     * The output will include the full local date and the chronology ID.
     *
     * @return the formatted date, not null
     */
    @Override
    public String toString() {
        // getLong() reduces chances of exceptions in toString()
        long yoe = getLong(YEAR_OF_ERA);
        long moy = getLong(MONTH_OF_YEAR);
        long dom = getLong(DAY_OF_MONTH);
        StringBuilder buf = new StringBuilder(30);
        buf.append(getChronology().toString())
                .append(" ")
                .append(getEra())
                .append(" ")
                .append(yoe)
                .append(moy < 10 ? "-0" : "-").append(moy)
                .append(dom < 10 ? "-0" : "-").append(dom);
        return buf.toString();
    }

}