# Class XMLGregorianCalendar

java.lang.Object
javax.xml.datatype.XMLGregorianCalendar

All Implemented Interfaces:
  `Cloneable`

public abstract class XMLGregorianCalendar extends Object implements Cloneable

Representation for W3C XML Schema 1.0 date/time datatypes. Specifically, these date/time datatypes are `DatatypeConstants.DATETIME`, `DatatypeConstants.TIME`, `DatatypeConstants.DATE`, `DatatypeConstants.GYEARMONTH`, `DatatypeConstants.GMONTHDAY`, `DatatypeConstants.GYEAR`, `DatatypeConstants.GMONTH`, and `DatatypeConstants.GDAY` defined in the XML Namespace `"http://www.w3.org/2001/XMLSchema"`. These datatypes are normatively defined in W3C XML Schema 1.0 Part 2, Section 3.2.7-14.

The table below defines the mapping between XML Schema 1.0 date/time datatype fields and this class' fields. It also summarizes the value constraints for the date and time fields defined in W3C XML Schema 1.0 Part 2, Appendix D, ISO 8601 Date and Time Formats.

Date/Time Datatype Field Mapping Between XML Schema 1.0 and Java Representation
XML Schema 1.0 datatype field | Related XMLGregorianCalendar Accessor(s) | Value Range
--- | --- | ---
year | `getYear()` + `getEon()` or `getEonAndYear()` | `getYear()` is a value between -(10^9-1) to (10^9)-1 or `DatatypeConstants.FIELD_UNDEFINED`. `getEon()` is high order year value in billion of years. `getEon()` has values greater than or equal to (10^9) or less than or equal to -(10^9). A value of null indicates field is undefined. Given that XML Schema 1.0 errata states that the year zero will be a valid lexical value in a future version of XML Schema, this class allows the year field to be set to zero. Otherwise, the year field value is handled exactly as described in the errata and [ISO-8601-1988]. Note that W3C XML Schema 1.0 validation does not allow for the year field to have a value of zero.
month | `getMonth()` | 1 to 12 or `DatatypeConstants.FIELD_UNDEFINED`
day | `getDay()` | Independent of month, max range is 1 to 31 or `DatatypeConstants.FIELD_UNDEFINED`. The normative value constraint stated relative to month field's value is in W3C XML Schema 1.0 Part 2, Appendix D.
hour | `getHour()` | 0 to 23 or `DatatypeConstants.FIELD_UNDEFINED`. An hour value of 24 is allowed to be set in the lexical space provided the minute and second field values are zero. However, an hour value of 24 is not allowed in value space and will be transformed to represent the value of the first instance of the following day as per XML Schema Part 2: Datatypes Second Edition, 3.2 Primitive datatypes.
minute | `getMinute()` | 0 to 59 or `DatatypeConstants.FIELD_UNDEFINED`
second | `getSecond()` + `getMillisecond()`/1000 or `getSecond()` + `getFractionalSecond()` | `getSecond()` from 0 to 60 or `DatatypeConstants.FIELD_UNDEFINED`. (Note: 60 only allowable for leap second.) `getFractionalSecond()` allows for infinite precision over the range from 0.0 to 1.0 when the `getSecond()` is defined. `FractionalSecond` is optional and has a value of `null` when it is undefined. `getMillisecond()` is the convenience millisecond precision of value of `getFractionalSecond()`.
timezone | `getTimezone()` | Number of minutes or `DatatypeConstants.FIELD_UNDEFINED`. Value range from -14 hours (-14 * 60 minutes) to 14 hours (14 * 60 minutes).

All maximum value space constraints listed for the fields in the table above are checked by factory methods, `DatatypeFactory`, setter methods and parse methods of this class. `IllegalArgumentException` is thrown when a parameter's value is outside the value constraint for the field or if the composite values constitute an invalid XMLGregorianCalendar instance (for example, if the 31st of June is specified).

The following operations are defined for this class:

- accessors/mutators for independent date/time fields
- conversion between this class and W3C XML Schema 1.0 lexical representation, `toString()`, `DatatypeFactory.newXMLGregorianCalendar(String lexicalRepresentation)`
- conversion between this class and `GregorianCalendar`, `toGregorianCalendar(java.util.TimeZone timezone, java.util.Locale aLocale, XMLGregorianCalendar defaults)`, `DatatypeFactory`
- partial order relation comparator method, `compare(XMLGregorianCalendar xmlGregorianCalendar)`
- `equals(Object)` defined relative to `compare(XMLGregorianCalendar xmlGregorianCalendar)`.
- addition operation with `Duration` instance as defined in W3C XML Schema 1.0 Part 2, Appendix E, Adding durations to dateTimes.

Since:
  1.5
See Also:
  - `Duration`
  - `DatatypeFactory`

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `XMLGregorianCalendar()`
  Default no-arg constructor.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `abstract void`
  `add(Duration duration)`
  Add `duration` to this instance.
  `abstract void`
  `clear()`
  Unset all fields to undefined.
  `abstract Object`
  `clone()`
  Creates and returns a copy of this object.
  `abstract int`
  `compare(XMLGregorianCalendar xmlGregorianCalendar)`
  Compare two instances of W3C XML Schema 1.0 date/time datatypes according to partial order relation defined in W3C XML Schema 1.0 Part 2, Section 3.2.7.3, Order relation on dateTime.
  `boolean`
  `equals(Object obj)`
  Compares this calendar to the specified object.
  `abstract int`
  `getDay()`
  Returns the day of month or `DatatypeConstants.FIELD_UNDEFINED`.
  `abstract BigInteger`
  `getEon()`
  Returns the high order component for XML Schema 1.0 dateTime datatype field for `year`.
  `abstract BigInteger`
  `getEonAndYear()`
  Returns the XML Schema 1.0 dateTime datatype field for `year`.
  `abstract BigDecimal`
  `getFractionalSecond()`
  Returns fractional seconds.
  `abstract int`
  `getHour()`
  Returns the hour of day or `DatatypeConstants.FIELD_UNDEFINED` if this field is not defined.
  `int`
  `getMillisecond()`
  Returns the millisecond precision of `getFractionalSecond()`.
  `abstract int`
  `getMinute()`
  Returns the minute of hour or `DatatypeConstants.FIELD_UNDEFINED` if this field is not defined.
  `abstract int`
  `getMonth()`
  Returns the month of this calendar or `DatatypeConstants.FIELD_UNDEFINED`.
  `abstract int`
  `getSecond()`
  Returns the second of minute or `DatatypeConstants.FIELD_UNDEFINED` if this field is not defined.
  `abstract int`
  `getTimezone()`
  Returns the Timezone offset in minutes or `DatatypeConstants.FIELD_UNDEFINED` if this optional field is not defined.
  `abstract TimeZone`
  `getTimeZone(int defaultZoneoffset)`
  Returns a `java.util.TimeZone` for this class.
  `abstract QName`
  `getXMLSchemaType()`
  Return the name of the XML Schema date/time type that this instance maps to.
  `abstract int`
  `getYear()`
  Returns the low order component for XML Schema 1.0 dateTime datatype field for `year` or `DatatypeConstants.FIELD_UNDEFINED`.
  `int`
  `hashCode()`
  Returns a hash code consistent with the definition of the equals method.
  `abstract boolean`
  `isValid()`
  Validate instance by `getXMLSchemaType()` constraints.
  `abstract XMLGregorianCalendar`
  `normalize()`
  Normalize this instance to UTC.
  `abstract void`
  `reset()`
  Reset this `XMLGregorianCalendar` to its original values.
  `abstract void`
  `setDay(int day)`
  Set days in month.
  `abstract void`
  `setFractionalSecond(BigDecimal fractional)`
  Set fractional seconds.
  `abstract void`
  `setHour(int hour)`
  Set hours.
  `abstract void`
  `setMillisecond(int millisecond)`
  Set milliseconds.
  `abstract void`
  `setMinute(int minute)`
  Set minutes.
  `abstract void`
  `setMonth(int month)`
  Set month.
  `abstract void`
  `setSecond(int second)`
  Set seconds.
  `void`
  `setTime(int hour, int minute, int second)`
  Set time as one unit.
  `void`
  `setTime(int hour, int minute, int second, int millisecond)`
  Set time as one unit, including optional milliseconds.
  `void`
  `setTime(int hour, int minute, int second, BigDecimal fractional)`
  Set time as one unit, including the optional infinite precision fractional seconds.
  `abstract void`
  `setTimezone(int offset)`
  Set the number of minutes in the timezone offset.
  `abstract void`
  `setYear(int year)`
  Set year of XSD `dateTime` year field.
  `abstract void`
  `setYear(BigInteger year)`
  Set low and high order component of XSD `dateTime` year field.
  `abstract GregorianCalendar`
  `toGregorianCalendar()`
  Convert this `XMLGregorianCalendar` to a `GregorianCalendar`.
  `abstract GregorianCalendar`
  `toGregorianCalendar(TimeZone timezone, Locale aLocale, XMLGregorianCalendar defaults)`
  Convert this `XMLGregorianCalendar` along with provided parameters to a `GregorianCalendar` instance.
  `String`
  `toString()`
  Returns a `String` representation of this `XMLGregorianCalendar` `Object`.
  `abstract String`
  `toXMLFormat()`
  Return the lexical representation of `this` instance.

  ### Methods declared in class java.lang.Object

  `finalize, getClass, notify, notifyAll, wait, wait, wait`

- ## Constructor Details

  - ### XMLGregorianCalendar

    public XMLGregorianCalendar()
    Default no-arg constructor.

    Note: Always use the `DatatypeFactory` to construct an instance of `XMLGregorianCalendar`. The constructor on this class cannot be guaranteed to produce an object with a consistent state and may be removed in the future.

- ## Method Details

  - ### clear

    public abstract void clear()
    Unset all fields to undefined.

    Set all int fields to `DatatypeConstants.FIELD_UNDEFINED` and reference fields to null.

  - ### reset

    public abstract void reset()
    Reset this `XMLGregorianCalendar` to its original values.

    `XMLGregorianCalendar` is reset to the same values as when it was created with `DatatypeFactory.newXMLGregorianCalendar()`, `DatatypeFactory.newXMLGregorianCalendar(String lexicalRepresentation)`, `DatatypeFactory.newXMLGregorianCalendar(BigInteger year, int month, int day, int hour, int minute, int second, BigDecimal fractionalSecond, int timezone)`, `DatatypeFactory.newXMLGregorianCalendar(int year, int month, int day, int hour, int minute, int second, int millisecond, int timezone)`, `DatatypeFactory.newXMLGregorianCalendar(GregorianCalendar cal)`, `DatatypeFactory.newXMLGregorianCalendarDate(int year, int month, int day, int timezone)`, `DatatypeFactory.newXMLGregorianCalendarTime(int hours, int minutes, int seconds, int timezone)`, `DatatypeFactory.newXMLGregorianCalendarTime(int hours, int minutes, int seconds, BigDecimal fractionalSecond, int timezone)` or `DatatypeFactory.newXMLGregorianCalendarTime(int hours, int minutes, int seconds, int milliseconds, int timezone)`.

    `reset()` is designed to allow the reuse of existing `XMLGregorianCalendar`s thus saving resources associated with the creation of new `XMLGregorianCalendar`s.

  - ### setYear

    public abstract void setYear(BigInteger year)
    Set low and high order component of XSD `dateTime` year field.

    Unset this field by invoking the setter with a parameter value of `null`.

    Parameters:
      `year` - value constraints summarized in year field of date/time field mapping table.
    Throws:
      `IllegalArgumentException` - if `year` parameter is outside value constraints for the field as specified in date/time field mapping table.

  - ### setYear

    public abstract void setYear(int year)
    Set year of XSD `dateTime` year field.

    Unset this field by invoking the setter with a parameter value of `DatatypeConstants.FIELD_UNDEFINED`.

    Note: if the absolute value of the `year` parameter is less than 10^9, the eon component of the XSD year field is set to `null` by this method.

    Parameters:
      `year` - value constraints are summarized in year field of date/time field mapping table. If year is `DatatypeConstants.FIELD_UNDEFINED`, then eon is set to `null`.

  - ### setMonth

    public abstract void setMonth(int month)
    Set month.

    Unset this field by invoking the setter with a parameter value of `DatatypeConstants.FIELD_UNDEFINED`.

    Parameters:
      `month` - value constraints summarized in month field of date/time field mapping table.
    Throws:
      `IllegalArgumentException` - if `month` parameter is outside value constraints for the field as specified in date/time field mapping table.

  - ### setDay

    public abstract void setDay(int day)
    Set days in month.

    Unset this field by invoking the setter with a parameter value of `DatatypeConstants.FIELD_UNDEFINED`.

    Parameters:
      `day` - value constraints summarized in day field of date/time field mapping table.
    Throws:
      `IllegalArgumentException` - if `day` parameter is outside value constraints for the field as specified in date/time field mapping table.

  - ### setTimezone

    public abstract void setTimezone(int offset)
    Set the number of minutes in the timezone offset.

    Unset this field by invoking the setter with a parameter value of `DatatypeConstants.FIELD_UNDEFINED`.

    Parameters:
      `offset` - value constraints summarized in timezone field of date/time field mapping table.
    Throws:
      `IllegalArgumentException` - if `offset` parameter is outside value constraints for the field as specified in date/time field mapping table.

  - ### setTime

    public void setTime(int hour, int minute, int second)
    Set time as one unit.
    Parameters:
      `hour` - value constraints are summarized in hour field of date/time field mapping table.
      `minute` - value constraints are summarized in minute field of date/time field mapping table.
      `second` - value constraints are summarized in second field of date/time field mapping table.
    Throws:
      `IllegalArgumentException` - if any parameter is outside value constraints for the field as specified in date/time field mapping table.
    See Also:
      - `setTime(int, int, int, BigDecimal)`

  - ### setHour

    public abstract void setHour(int hour)
    Set hours.

    Unset this field by invoking the setter with a parameter value of `DatatypeConstants.FIELD_UNDEFINED`.

    Parameters:
      `hour` - value constraints summarized in hour field of date/time field mapping table.
    Throws:
      `IllegalArgumentException` - if `hour` parameter is outside value constraints for the field as specified in date/time field mapping table.

  - ### setMinute

    public abstract void setMinute(int minute)
    Set minutes.

    Unset this field by invoking the setter with a parameter value of `DatatypeConstants.FIELD_UNDEFINED`.

    Parameters:
      `minute` - value constraints summarized in minute field of date/time field mapping table.
    Throws:
      `IllegalArgumentException` - if `minute` parameter is outside value constraints for the field as specified in date/time field mapping table.

  - ### setSecond

    public abstract void setSecond(int second)
    Set seconds.

    Unset this field by invoking the setter with a parameter value of `DatatypeConstants.FIELD_UNDEFINED`.

    Parameters:
      `second` - value constraints summarized in second field of date/time field mapping table.
    Throws:
      `IllegalArgumentException` - if `second` parameter is outside value constraints for the field as specified in date/time field mapping table.

  - ### setMillisecond

    public abstract void setMillisecond(int millisecond)
    Set milliseconds.

    Unset this field by invoking the setter with a parameter value of `DatatypeConstants.FIELD_UNDEFINED`.

    Parameters:
      `millisecond` - value constraints summarized in second field of date/time field mapping table.
    Throws:
      `IllegalArgumentException` - if `millisecond` parameter is outside value constraints for the field as specified in date/time field mapping table.

  - ### setFractionalSecond

    public abstract void setFractionalSecond(BigDecimal fractional)
    Set fractional seconds.

    Unset this field by invoking the setter with a parameter value of `null`.

    Parameters:
      `fractional` - value constraints summarized in second field of date/time field mapping table.
    Throws:
      `IllegalArgumentException` - if `fractional` parameter is outside value constraints for the field as specified in date/time field mapping table.

  - ### setTime

    public void setTime(int hour, int minute, int second, BigDecimal fractional)
    Set time as one unit, including the optional infinite precision fractional seconds.
    Parameters:
      `hour` - value constraints are summarized in hour field of date/time field mapping table.
      `minute` - value constraints are summarized in minute field of date/time field mapping table.
      `second` - value constraints are summarized in second field of date/time field mapping table.
      `fractional` - value of `null` indicates this optional field is not set.
    Throws:
      `IllegalArgumentException` - if any parameter is outside value constraints for the field as specified in date/time field mapping table.

  - ### setTime

    public void setTime(int hour, int minute, int second, int millisecond)
    Set time as one unit, including optional milliseconds.
    Parameters:
      `hour` - value constraints are summarized in hour field of date/time field mapping table.
      `minute` - value constraints are summarized in minute field of date/time field mapping table.
      `second` - value constraints are summarized in second field of date/time field mapping table.
      `millisecond` - value of `DatatypeConstants.FIELD_UNDEFINED` indicates this optional field is not set.
    Throws:
      `IllegalArgumentException` - if any parameter is outside value constraints for the field as specified in date/time field mapping table.

  - ### getEon

    public abstract BigInteger getEon()
    Returns the high order component for XML Schema 1.0 dateTime datatype field for `year`. `null` if this optional part of the year field is not defined.

    Value constraints for this value are summarized in year field of date/time field mapping table.

    Returns:
      The eon of this `XMLGregorianCalendar`. The value returned is an integer multiple of 10^9.
    See Also:
      - `getYear()`
      - `getEonAndYear()`

  - ### getYear

    public abstract int getYear()
    Returns the low order component for XML Schema 1.0 dateTime datatype field for `year` or `DatatypeConstants.FIELD_UNDEFINED`.

    Value constraints for this value are summarized in year field of date/time field mapping table.

    Returns:
      The year of this `XMLGregorianCalendar`.
    See Also:
      - `getEon()`
      - `getEonAndYear()`

  - ### getEonAndYear

    public abstract BigInteger getEonAndYear()
    Returns the XML Schema 1.0 dateTime datatype field for `year`.

    Value constraints for this value are summarized in year field of date/time field mapping table.

    Returns:
      sum of `eon` and `BigInteger.valueOf(year)` when both fields are defined. When only `year` is defined, return it. When both `eon` and `year` are not defined, return `null`.
    See Also:
      - `getEon()`
      - `getYear()`

  - ### getMonth

    public abstract int getMonth()
    Returns the month of this calendar or `DatatypeConstants.FIELD_UNDEFINED`.

    Value constraints for this value are summarized in month field of date/time field mapping table.

    Returns:
      The month of this `XMLGregorianCalendar`, from 1 to 12.

  - ### getDay

    public abstract int getDay()
    Returns the day of month or `DatatypeConstants.FIELD_UNDEFINED`.

    Value constraints for this value are summarized in day field of date/time field mapping table.

    Returns:
      The day of month of this `XMLGregorianCalendar`, from 1 to 31.
    See Also:
      - `setDay(int)`

  - ### getTimezone

    public abstract int getTimezone()
    Returns the Timezone offset in minutes or `DatatypeConstants.FIELD_UNDEFINED` if this optional field is not defined.

    Value constraints for this value are summarized in timezone field of date/time field mapping table.

    Returns:
      The Timezone offset in minutes of this `XMLGregorianCalendar`.
    See Also:
      - `setTimezone(int)`

  - ### getHour

    public abstract int getHour()
    Returns the hour of day or `DatatypeConstants.FIELD_UNDEFINED` if this field is not defined.

    Value constraints for this value are summarized in hour field of date/time field mapping table.

    Returns:
      The hour of day of this `XMLGregorianCalendar`, from 0 to 23.
    See Also:
      - `setTime(int, int, int)`

  - ### getMinute

    public abstract int getMinute()
    Returns the minute of hour or `DatatypeConstants.FIELD_UNDEFINED` if this field is not defined.

    Value constraints for this value are summarized in minute field of date/time field mapping table.

    Returns:
      The minute of hour of this `XMLGregorianCalendar`, from 0 to 59.
    See Also:
      - `setTime(int, int, int)`

  - ### getSecond

    public abstract int getSecond()
    Returns the second of minute or `DatatypeConstants.FIELD_UNDEFINED` if this field is not defined. When this field is not defined, the optional xs:dateTime fractional seconds field, represented by `getFractionalSecond()` and `getMillisecond()`, must not be defined.

    Value constraints for this value are summarized in second field of date/time field mapping table.

    Returns:
      The second of minute of this `XMLGregorianCalendar`, from 0 to 59.
    See Also:
      - `getFractionalSecond()`
      - `getMillisecond()`
      - `setTime(int, int, int)`

  - ### getMillisecond

    public int getMillisecond()
    Returns the millisecond precision of `getFractionalSecond()`.

    This method represents a convenience accessor to infinite precision fractional second value returned by `getFractionalSecond()`. The returned value is the rounded down to milliseconds value of `getFractionalSecond()`. When `getFractionalSecond()` returns `null`, this method must return `DatatypeConstants.FIELD_UNDEFINED`.

    Value constraints for this value are summarized in second field of date/time field mapping table.

    Returns:
      The millisecond precision of this `XMLGregorianCalendar`.
    See Also:
      - `getFractionalSecond()`
      - `setTime(int, int, int)`

  - ### getFractionalSecond

    public abstract BigDecimal getFractionalSecond()
    Returns fractional seconds.

    `null` is returned when this optional field is not defined.

    Value constraints are detailed in second field of date/time field mapping table.

    This optional field can only have a defined value when the xs:dateTime second field, represented by `getSecond()`, does not return `DatatypeConstants.FIELD_UNDEFINED`.

    Returns:
      Fractional seconds of this `XMLGregorianCalendar`.
    See Also:
      - `getSecond()`
      - `setTime(int, int, int, BigDecimal)`

  - ### compare

    public abstract int compare(XMLGregorianCalendar xmlGregorianCalendar)
    Compare two instances of W3C XML Schema 1.0 date/time datatypes according to partial order relation defined in W3C XML Schema 1.0 Part 2, Section 3.2.7.3, Order relation on dateTime.

    `xsd:dateTime` datatype field mapping to accessors of this class are defined in date/time field mapping table.

    Parameters:
      `xmlGregorianCalendar` - Instance of `XMLGregorianCalendar` to compare
    Returns:
      The relationship between `this` `XMLGregorianCalendar` and the specified `xmlGregorianCalendar` as `DatatypeConstants.LESSER`, `DatatypeConstants.EQUAL`, `DatatypeConstants.GREATER` or `DatatypeConstants.INDETERMINATE`.
    Throws:
      `NullPointerException` - if `xmlGregorianCalendar` is null.

  - ### normalize

    public abstract XMLGregorianCalendar normalize()
    Normalize this instance to UTC.

    2000-03-04T23:00:00+03:00 normalizes to 2000-03-04T20:00:00Z

    Implements W3C XML Schema Part 2, Section 3.2.7.3 (A).

    Returns:
      `this` `XMLGregorianCalendar` normalized to UTC.

  - ### equals

    public boolean equals(Object obj)
    Compares this calendar to the specified object. The result is `true` if and only if the argument is not null and is an `XMLGregorianCalendar` object that represents the same instant in time as this object.
    Overrides:
      `equals` in class `Object`
    Parameters:
      `obj` - to compare.
    Returns:
      `true` when `obj` is an instance of `XMLGregorianCalendar` and `compare(XMLGregorianCalendar obj)` returns `DatatypeConstants.EQUAL`, otherwise `false`.
    See Also:
      - `Object.hashCode()`
      - `HashMap`

  - ### hashCode

    public int hashCode()
    Returns a hash code consistent with the definition of the equals method.
    Overrides:
      `hashCode` in class `Object`
    Returns:
      hash code of this object.
    See Also:
      - `Object.equals(java.lang.Object)`
      - `System.identityHashCode(java.lang.Object)`

  - ### toXMLFormat

    public abstract String toXMLFormat()
    Return the lexical representation of `this` instance. The format is specified in XML Schema 1.0 Part 2, Section 3.2.[7-14].1, Lexical Representation".

    Specific target lexical representation format is determined by `getXMLSchemaType()`.

    Returns:
      XML, as `String`, representation of this `XMLGregorianCalendar`
    Throws:
      `IllegalStateException` - if the combination of set fields does not match one of the eight defined XML Schema builtin date/time datatypes.

  - ### getXMLSchemaType

    public abstract QName getXMLSchemaType()
    Return the name of the XML Schema date/time type that this instance maps to. Type is computed based on fields that are set.

    Required fields for XML Schema 1.0 Date/Time Datatypes.
    (timezone is optional for all date/time datatypes)
    Datatype | year | month | day | hour | minute | second
    --- | --- | --- | --- | --- | --- | ---
    `DatatypeConstants.DATETIME` | X | X | X | X | X | X
    `DatatypeConstants.DATE` | X | X | X |  |  |
    `DatatypeConstants.TIME` |  |  |  | X | X | X
    `DatatypeConstants.GYEARMONTH` | X | X |  |  |  |
    `DatatypeConstants.GMONTHDAY` |  | X | X |  |  |
    `DatatypeConstants.GYEAR` | X |  |  |  |  |
    `DatatypeConstants.GMONTH` |  | X |  |  |  |
    `DatatypeConstants.GDAY` |  |  | X |  |  |

    Returns:
      One of the following class constants: `DatatypeConstants.DATETIME`, `DatatypeConstants.TIME`, `DatatypeConstants.DATE`, `DatatypeConstants.GYEARMONTH`, `DatatypeConstants.GMONTHDAY`, `DatatypeConstants.GYEAR`, `DatatypeConstants.GMONTH` or `DatatypeConstants.GDAY`.
    Throws:
      `IllegalStateException` - if the combination of set fields does not match one of the eight defined XML Schema builtin date/time datatypes.

  - ### toString

    public String toString()
    Returns a `String` representation of this `XMLGregorianCalendar` `Object`.

    The result is a lexical representation generated by `toXMLFormat()`.

    Overrides:
      `toString` in class `Object`
    Returns:
      A non-`null` valid `String` representation of this `XMLGregorianCalendar`.
    Throws:
      `IllegalStateException` - if the combination of set fields does not match one of the eight defined XML Schema builtin date/time datatypes.
    See Also:
      - `toXMLFormat()`

  - ### isValid

    public abstract boolean isValid()
    Validate instance by `getXMLSchemaType()` constraints.
    Returns:
      true if data values are valid.

  - ### add

    public abstract void add(Duration duration)
    Add `duration` to this instance.

    The computation is specified in XML Schema 1.0 Part 2, Appendix E, Adding durations to dateTimes. date/time field mapping table defines the mapping from XML Schema 1.0 `dateTime` fields to this class' representation of those fields.

    Parameters:
      `duration` - Duration to add to this `XMLGregorianCalendar`.
    Throws:
      `NullPointerException` - when `duration` parameter is `null`.

  - ### toGregorianCalendar

    public abstract GregorianCalendar toGregorianCalendar()
    Convert this `XMLGregorianCalendar` to a `GregorianCalendar`.

    When `this` instance has an undefined field, this conversion relies on the `java.util.GregorianCalendar` default for its corresponding field. A notable difference between XML Schema 1.0 date/time datatypes and `java.util.GregorianCalendar` is that Timezone value is optional for date/time datatypes and it is a required field for `java.util.GregorianCalendar`. See javadoc for `java.util.TimeZone.getDefault()` on how the default is determined. To explicitly specify the `TimeZone` instance, see `toGregorianCalendar(TimeZone, Locale, XMLGregorianCalendar)`.

    Field by Field Conversion from this class to `java.util.GregorianCalendar`
    `java.util.GregorianCalendar` field | `javax.xml.datatype.XMLGregorianCalendar` field
    --- | ---
    `ERA` | `getEonAndYear()``.signum() < 0 ? GregorianCalendar.BC : GregorianCalendar.AD`
    `YEAR` | `getEonAndYear()``.abs().intValue()`*
    `MONTH` | `getMonth()` - `DatatypeConstants.JANUARY` + `Calendar.JANUARY`
    `DAY_OF_MONTH` | `getDay()`
    `HOUR_OF_DAY` | `getHour()`
    `MINUTE` | `getMinute()`
    `SECOND` | `getSecond()`
    `MILLISECOND` | get millisecond order from `getFractionalSecond()`*
    `GregorianCalendar.setTimeZone(TimeZone)` | `getTimezone()` formatted into Custom timezone id

    * designates possible loss of precision during the conversion due to source datatype having higher precision than target datatype.

    To ensure consistency in conversion implementations, the new `GregorianCalendar` should be instantiated in following manner.

    - Using `timeZone` value as defined above, create a new `java.util.GregorianCalendar(timeZone,Locale.getDefault())`.
    - Initialize all GregorianCalendar fields by calling `Calendar.clear()`.
    - Obtain a pure Gregorian Calendar by invoking `GregorianCalendar.setGregorianChange( new Date(Long.MIN_VALUE))`.
    - Its fields ERA, YEAR, MONTH, DAY_OF_MONTH, HOUR_OF_DAY, MINUTE, SECOND and MILLISECOND are set using the method `Calendar.set(int,int)`
    Returns:
      An instance of `GregorianCalendar`.
    See Also:
      - `toGregorianCalendar(java.util.TimeZone, java.util.Locale, XMLGregorianCalendar)`

  - ### toGregorianCalendar

    public abstract GregorianCalendar toGregorianCalendar(TimeZone timezone, Locale aLocale, XMLGregorianCalendar defaults)
    Convert this `XMLGregorianCalendar` along with provided parameters to a `GregorianCalendar` instance.

    Since XML Schema 1.0 date/time datetypes has no concept of timezone ids or daylight savings timezone ids, this conversion operation allows the user to explicitly specify one with `timezone` parameter.

    To compute the return value's `TimeZone` field,

    - when parameter `timeZone` is non-null, it is the timezone field.
    - else when `this.getTimezone() != FIELD_UNDEFINED`, create a `java.util.TimeZone` with a custom timezone id using the `this.getTimezone()`.
    - else when `defaults.getTimezone() != FIELD_UNDEFINED`, create a `java.util.TimeZone` with a custom timezone id using `defaults.getTimezone()`.
    - else use the `GregorianCalendar` default timezone value for the host is defined as specified by `java.util.TimeZone.getDefault()`.

    To ensure consistency in conversion implementations, the new `GregorianCalendar` should be instantiated in following manner.

    - Create a new `java.util.GregorianCalendar(TimeZone, Locale)` with TimeZone set as specified above and the `Locale` parameter.
    - Initialize all GregorianCalendar fields by calling `Calendar.clear()`
    - Obtain a pure Gregorian Calendar by invoking `GregorianCalendar.setGregorianChange( new Date(Long.MIN_VALUE))`.
    - Its fields ERA, YEAR, MONTH, DAY_OF_MONTH, HOUR_OF_DAY, MINUTE, SECOND and MILLISECOND are set using the method `Calendar.set(int,int)`
    Parameters:
      `timezone` - provide Timezone. `null` is a legal value.
      `aLocale` - provide explicit Locale. Use default GregorianCalendar locale if value is `null`.
      `defaults` - provide default field values to use when corresponding field for this instance is FIELD_UNDEFINED or null. If `defaults`is `null` or a field within the specified `defaults` is undefined, just use `java.util.GregorianCalendar` defaults.
    Returns:
      a java.util.GregorianCalendar conversion of this instance.

  - ### getTimeZone

    public abstract TimeZone getTimeZone(int defaultZoneoffset)
    Returns a `java.util.TimeZone` for this class.

    If timezone field is defined for this instance, returns TimeZone initialized with custom timezone id of zoneoffset. If timezone field is undefined, try the defaultZoneoffset that was passed in. If defaultZoneoffset is FIELD_UNDEFINED, return default timezone for this host. (Same default as java.util.GregorianCalendar).

    Parameters:
      `defaultZoneoffset` - default zoneoffset if this zoneoffset is `DatatypeConstants.FIELD_UNDEFINED`.
    Returns:
      TimeZone for this.

  - ### clone

    public abstract Object clone()
    Creates and returns a copy of this object.
    Overrides:
      `clone` in class `Object`
    Returns:
      copy of this `Object`
    See Also:
      - `Cloneable`