JulianFields.java

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 * Copyright (c) 2012, Stephen Colebourne & Michael Nascimento Santos
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package java.time.temporal;

import static java.time.temporal.ChronoField.EPOCH_DAY;
import static java.time.temporal.ChronoUnit.DAYS;
import static java.time.temporal.ChronoUnit.FOREVER;

import java.time.DateTimeException;
import java.util.Collections;
import java.util.Map;

/**
 * A set of date fields that provide access to Julian Days.
 * <p>
 * The Julian Day is a standard way of expressing date and time commonly used in the scientific community.
 * It is expressed as a decimal number of whole days where days start at midday.
 * This class represents variations on Julian Days that count whole days from midnight.
 * <p>
 * The fields are implemented relative to {@link ChronoField#EPOCH_DAY EPOCH_DAY}.
 * The fields are supported, and can be queried and set if {@code EPOCH_DAY} is available.
 * The fields work with all chronologies.
 *
 * <h3>Specification for implementors</h3>
 * This is an immutable and thread-safe class.
 *
 * @since 1.8
 */
public final class JulianFields {

    /**
     * The offset from Julian to EPOCH DAY.
     */
    private static final long JULIAN_DAY_OFFSET = 2440588L;

    /**
     * Julian Day field.
     * <p>
     * This is an integer-based version of the Julian Day Number.
     * Julian Day is a well-known system that represents the count of whole days since day 0,
     * which is defined to be January 1, 4713 BCE in the Julian calendar, and -4713-11-24 Gregorian.
     * The field  has "JulianDay" as 'name', and 'DAYS' as 'baseUnit'.
     * The field always refers to the local date-time, ignoring the offset or zone.
     * <p>
     * For date-times, 'JULIAN_DAY.getFrom()' assumes the same value from
     * midnight until just before the next midnight.
     * When 'JULIAN_DAY.adjustInto()' is applied to a date-time, the time of day portion remains unaltered.
     * 'JULIAN_DAY.adjustInto()' and 'JULIAN_DAY.getFrom()' only apply to {@code Temporal} objects that
     * can be converted into {@link ChronoField#EPOCH_DAY}.
     * A {@link DateTimeException} is thrown for any other type of object.
     * <p>
     * <h3>Astronomical and Scientific Notes</h3>
     * The standard astronomical definition uses a fraction to indicate the time-of-day,
     * thus 3.25 would represent the time 18:00, since days start at midday.
     * This implementation uses an integer and days starting at midnight.
     * The integer value for the Julian Day Number is the astronomical Julian Day value at midday
     * of the date in question.
     * This amounts to the astronomical Julian Day, rounded to an integer {@code JDN = floor(JD + 0.5)}.
     * <p>
     * <pre>
     *  | ISO date          |  Julian Day Number | Astronomical Julian Day |
     *  | 1970-01-01T00:00  |         2,440,588  |         2,440,587.5     |
     *  | 1970-01-01T06:00  |         2,440,588  |         2,440,587.75    |
     *  | 1970-01-01T12:00  |         2,440,588  |         2,440,588.0     |
     *  | 1970-01-01T18:00  |         2,440,588  |         2,440,588.25    |
     *  | 1970-01-02T00:00  |         2,440,589  |         2,440,588.5     |
     *  | 1970-01-02T06:00  |         2,440,589  |         2,440,588.75    |
     *  | 1970-01-02T12:00  |         2,440,589  |         2,440,589.0     |
     * </pre>
     * <p>
     * Julian Days are sometimes taken to imply Universal Time or UTC, but this
     * implementation always uses the Julian Day number for the local date,
     * regardless of the offset or time-zone.
     */
    public static final TemporalField JULIAN_DAY = Field.JULIAN_DAY;

    /**
     * Modified Julian Day field.
     * <p>
     * This is an integer-based version of the Modified Julian Day Number.
     * Modified Julian Day (MJD) is a well-known system that counts days continuously.
     * It is defined relative to astronomical Julian Day as  {@code MJD = JD - 2400000.5}.
     * Each Modified Julian Day runs from midnight to midnight.
     * The field always refers to the local date-time, ignoring the offset or zone.
     * <p>
     * For date-times, 'MODIFIED_JULIAN_DAY.getFrom()' assumes the same value from
     * midnight until just before the next midnight.
     * When 'MODIFIED_JULIAN_DAY.adjustInto()' is applied to a date-time, the time of day portion remains unaltered.
     * 'MODIFIED_JULIAN_DAY.adjustInto()' and 'MODIFIED_JULIAN_DAY.getFrom()' only apply to {@code Temporal} objects
     * that can be converted into {@link ChronoField#EPOCH_DAY}.
     * A {@link DateTimeException} is thrown for any other type of object.
     * <p>
     * This implementation is an integer version of MJD with the decimal part rounded to floor.
     * <p>
     * <h3>Astronomical and Scientific Notes</h3>
     * <pre>
     *  | ISO date          | Modified Julian Day |      Decimal MJD |
     *  | 1970-01-01T00:00  |             40,587  |       40,587.0   |
     *  | 1970-01-01T06:00  |             40,587  |       40,587.25  |
     *  | 1970-01-01T12:00  |             40,587  |       40,587.5   |
     *  | 1970-01-01T18:00  |             40,587  |       40,587.75  |
     *  | 1970-01-02T00:00  |             40,588  |       40,588.0   |
     *  | 1970-01-02T06:00  |             40,588  |       40,588.25  |
     *  | 1970-01-02T12:00  |             40,588  |       40,588.5   |
     * </pre>
     * <p>
     * Modified Julian Days are sometimes taken to imply Universal Time or UTC, but this
     * implementation always uses the Modified Julian Day for the local date,
     * regardless of the offset or time-zone.
     */
    public static final TemporalField MODIFIED_JULIAN_DAY = Field.MODIFIED_JULIAN_DAY;

    /**
     * Rata Die field.
     * <p>
     * Rata Die counts whole days continuously starting day 1 at midnight at the beginning of 0001-01-01 (ISO).
     * The field always refers to the local date-time, ignoring the offset or zone.
     * <p>
     * For date-times, 'RATA_DIE.getFrom()' assumes the same value from
     * midnight until just before the next midnight.
     * When 'RATA_DIE.adjustInto()' is applied to a date-time, the time of day portion remains unaltered.
     * 'RATA_DIE.adjustInto()' and 'RATA_DIE.getFrom()' only apply to {@code Temporal} objects
     * that can be converted into {@link ChronoField#EPOCH_DAY}.
     * A {@link DateTimeException} is thrown for any other type of object.
     */
    public static final TemporalField RATA_DIE = Field.RATA_DIE;

    /**
     * Restricted constructor.
     */
    private JulianFields() {
        throw new AssertionError("Not instantiable");
    }

    /**
     * Implementation of JulianFields.  Each instance is a singleton.
     */
    private static enum Field implements TemporalField {
        JULIAN_DAY("JulianDay", DAYS, FOREVER, JULIAN_DAY_OFFSET),
        MODIFIED_JULIAN_DAY("ModifiedJulianDay", DAYS, FOREVER, 40587L),
        RATA_DIE("RataDie", DAYS, FOREVER, 719163L);

        private static final long serialVersionUID = -7501623920830201812L;

        private final transient String name;
        private final transient TemporalUnit baseUnit;
        private final transient TemporalUnit rangeUnit;
        private final transient ValueRange range;
        private final transient long offset;

        private Field(String name, TemporalUnit baseUnit, TemporalUnit rangeUnit, long offset) {
            this.name = name;
            this.baseUnit = baseUnit;
            this.rangeUnit = rangeUnit;
            this.range = ValueRange.of(-365243219162L + offset, 365241780471L + offset);
            this.offset = offset;
        }

        //-----------------------------------------------------------------------
        @Override
        public String getName() {
            return name;
        }

        @Override
        public TemporalUnit getBaseUnit() {
            return baseUnit;
        }

        @Override
        public TemporalUnit getRangeUnit() {
            return rangeUnit;
        }

        @Override
        public ValueRange range() {
            return range;
        }

        //-----------------------------------------------------------------------
        @Override
        public boolean isSupportedBy(TemporalAccessor temporal) {
            return temporal.isSupported(EPOCH_DAY);
        }

        @Override
        public ValueRange rangeRefinedBy(TemporalAccessor temporal) {
            if (isSupportedBy(temporal) == false) {
                throw new DateTimeException("Unsupported field: " + this);
            }
            return range();
        }

        @Override
        public long getFrom(TemporalAccessor temporal) {
            return temporal.getLong(EPOCH_DAY) + offset;
        }

        @SuppressWarnings("unchecked")
        @Override
        public <R extends Temporal> R adjustInto(R temporal, long newValue) {
            if (range().isValidValue(newValue) == false) {
                throw new DateTimeException("Invalid value: " + name + " " + newValue);
            }
            return (R) temporal.with(EPOCH_DAY, Math.subtractExact(newValue, offset));
        }

        //-----------------------------------------------------------------------
        @Override
        public Map<TemporalField, Long> resolve(TemporalAccessor temporal, long value) {
            return Collections.<TemporalField, Long>singletonMap(EPOCH_DAY, Math.subtractExact(value, offset));
        }

        //-----------------------------------------------------------------------
        @Override
        public String toString() {
            return name;
        }
    }
}