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  /*
   * $Id: Duration.java,v 1.10 2010-11-01 04:36:08 joehw Exp $
   * %W% %E%
   */
  package mf.javax.xml.datatype;
  
  import java.math.BigDecimal;
  import java.math.BigInteger;
  import java.util.Calendar;
  import java.util.Date;
  import java.util.GregorianCalendar;
  
  import mf.javax.xml.namespace.QName;
  
  /**
   * <p>Immutable representation of a time span as defined in
   * the W3C XML Schema 1.0 specification.</p>
   * <p/>
   * <p>A Duration object represents a period of Gregorian time,
   * which consists of six fields (years, months, days, hours,
   * minutes, and seconds) plus a sign (+/-) field.</p>
   * <p/>
   * <p>The first five fields have non-negative (>=0) integers or null
   * (which represents that the field is not set),
   * and the seconds field has a non-negative decimal or null.
   * A negative sign indicates a negative duration.</p>
   * <p/>
   * <p>This class provides a number of methods that make it easy
   * to use for the duration datatype of XML Schema 1.0 with
   * the errata.</p>
   * <p/>
   * <h2>Order relationship</h2>
   * <p>Duration objects only have partial order, where two values A and B
   * maybe either:</p>
   * <ol>
   * <li>A&lt;B (A is shorter than B)
   * <li>A&gt;B (A is longer than B)
   * <li>A==B   (A and B are of the same duration)
   * <li>A&lt;>B (Comparison between A and B is indeterminate)
   * </ol>
   * <p/>
   * <p>For example, 30 days cannot be meaningfully compared to one month.
   * The {@link #compare(Duration duration)} method implements this
   * relationship.</p>
   * <p/>
   * <p>See the {@link #isLongerThan(Duration)} method for details about
   * the order relationship among <code>Duration</code> objects.</p>
   * <p/>
   * <h2>Operations over Duration</h2>
   * <p>This class provides a set of basic arithmetic operations, such
   * as addition, subtraction and multiplication.
   * Because durations don't have total order, an operation could
   * fail for some combinations of operations. For example, you cannot
   * subtract 15 days from 1 month. See the javadoc of those methods
   * for detailed conditions where this could happen.</p>
   * <p/>
   * <p>Also, division of a duration by a number is not provided because
   * the <code>Duration</code> class can only deal with finite precision
   * decimal numbers. For example, one cannot represent 1 sec divided by 3.</p>
   * <p/>
   * <p>However, you could substitute a division by 3 with multiplying
   * by numbers such as 0.3 or 0.333.</p>
   * <p/>
   * <h2>Range of allowed values</h2>
   * <p/>
   * Because some operations of <code>Duration</code> rely on {@link Calendar}
   * even though {@link Duration} can hold very large or very small values,
   * some of the methods may not work correctly on such <code>Duration</code>s.
   * The impacted methods document their dependency on {@link Calendar}.
   *
   * @author <a href="mailto:Joseph.Fialli@Sun.COM">Joseph Fialli</a>
   * @author <a href="mailto:Kohsuke.Kawaguchi@Sun.com">Kohsuke Kawaguchi</a>
   * @author <a href="mailto:Jeff.Suttor@Sun.com">Jeff Suttor</a>
   * @author <a href="mailto:Sunitha.Reddy@Sun.com">Sunitha Reddy</a>
   * @version $Revision: 1.10 $, $Date: 2010-11-01 04:36:08 $
   * @see XMLGregorianCalendar#add(Duration)
   * @since 1.5
   */
  public abstract class Duration {
  
      /**
       * <p>Debugging <code>true</code> or <code>false</code>.</p>
       */
      private static final boolean DEBUG = true;
  
      /**
       * Default no-arg constructor.
       * <p/>
       * <p>Note: Always use the {@link DatatypeFactory} to
       * construct an instance of <code>Duration</code>.
       * The constructor on this class cannot be guaranteed to
       * produce an object with a consistent state and may be
       * removed in the future.</p>
       */
      public Duration() {
      }
  
      /**
       * <p>Calls the {@link Calendar#getTimeInMillis} method.
       * Prior to JDK1.4, this method was protected and therefore
       * cannot be invoked directly.</p>
       * <p/>
       * <p>TODO: In future, this should be replaced by <code>cal.getTimeInMillis()</code>.</p>
       *
       * @param cal <code>Calendar</code> to get time in milliseconds.
       * @return Milliseconds of <code>cal</code>.
       */
      private static long getCalendarTimeInMillis(final Calendar cal) {
          return cal.getTime().getTime();
      }
  
      /**
       * <p>Return the name of the XML Schema date/time type that this instance
       * maps to. Type is computed based on fields that are set,
       * i.e. {@link #isSet(DatatypeConstants.Field field)} == <code>true</code>.</p>
       * <p/>
       * <table border="2" rules="all" cellpadding="2">
       * <thead>
       * <tr>
       * <th align="center" colspan="7">
       * Required fields for XML Schema 1.0 Date/Time Datatypes.<br/>
       * <i>(timezone is optional for all date/time datatypes)</i>
       * </th>
       * </tr>
       * </thead>
       * <tbody>
       * <tr>
       * <td>Datatype</td>
       * <td>year</td>
       * <td>month</td>
       * <td>day</td>
       * <td>hour</td>
       * <td>minute</td>
       * <td>second</td>
       * </tr>
       * <tr>
       * <td>{@link DatatypeConstants#DURATION}</td>
       * <td>X</td>
       * <td>X</td>
       * <td>X</td>
       * <td>X</td>
       * <td>X</td>
       * <td>X</td>
       * </tr>
       * <tr>
       * <td>{@link DatatypeConstants#DURATION_DAYTIME}</td>
       * <td></td>
       * <td></td>
       * <td>X</td>
       * <td>X</td>
       * <td>X</td>
       * <td>X</td>
       * </tr>
       * <tr>
       * <td>{@link DatatypeConstants#DURATION_YEARMONTH}</td>
       * <td>X</td>
       * <td>X</td>
       * <td></td>
       * <td></td>
       * <td></td>
       * <td></td>
       * </tr>
       * </tbody>
       * </table>
       *
       * @return one of the following constants:
       * {@link DatatypeConstants#DURATION},
       * {@link DatatypeConstants#DURATION_DAYTIME} or
       * {@link DatatypeConstants#DURATION_YEARMONTH}.
       * @throws IllegalStateException If the combination of set fields does not match one of the XML Schema date/time datatypes.
       */
      public QName getXMLSchemaType() {
  
          boolean yearSet = isSet(DatatypeConstants.YEARS);
          boolean monthSet = isSet(DatatypeConstants.MONTHS);
          boolean daySet = isSet(DatatypeConstants.DAYS);
          boolean hourSet = isSet(DatatypeConstants.HOURS);
          boolean minuteSet = isSet(DatatypeConstants.MINUTES);
          boolean secondSet = isSet(DatatypeConstants.SECONDS);
  
          // DURATION
          if (yearSet
                  && monthSet
                  && daySet
                  && hourSet
                  && minuteSet
                  && secondSet) {
              return DatatypeConstants.DURATION;
          }
  
          // DURATION_DAYTIME
          if (!yearSet
                  && !monthSet
                  && daySet
                  && hourSet
                  && minuteSet
                  && secondSet) {
              return DatatypeConstants.DURATION_DAYTIME;
          }
  
          // DURATION_YEARMONTH
          if (yearSet
                  && monthSet
                  && !daySet
                  && !hourSet
                  && !minuteSet
                  && !secondSet) {
              return DatatypeConstants.DURATION_YEARMONTH;
          }
  
          // nothing matches
          throw new IllegalStateException(
                  "mf.javax.xml.datatype.Duration#getXMLSchemaType():"
                          + " this Duration does not match one of the XML Schema date/time datatypes:"
                          + " year set = " + yearSet
                          + " month set = " + monthSet
                          + " day set = " + daySet
                          + " hour set = " + hourSet
                          + " minute set = " + minuteSet
                          + " second set = " + secondSet
          );
      }
  
      /**
       * Returns the sign of this duration in -1,0, or 1.
       *
       * @return -1 if this duration is negative, 0 if the duration is zero,
       * and 1 if the duration is positive.
       */
      public abstract int getSign();
  
      /**
       * <p>Get the years value of this <code>Duration</code> as an <code>int</code> or <code>0</code> if not present.</p>
       * <p/>
       * <p><code>getYears()</code> is a convenience method for
       * {@link #getField(DatatypeConstants.Field field) getField(DatatypeConstants.YEARS)}.</p>
       * <p/>
       * <p>As the return value is an <code>int</code>, an incorrect value will be returned for <code>Duration</code>s
       * with years that go beyond the range of an <code>int</code>.
       * Use {@link #getField(DatatypeConstants.Field field) getField(DatatypeConstants.YEARS)} to avoid possible loss of precision.</p>
       *
       * @return If the years field is present, return its value as an <code>int</code>, else return <code>0</code>.
       */
      public int getYears() {
          return getField(DatatypeConstants.YEARS).intValue();
      }
  
      /**
       * Obtains the value of the MONTHS field as an integer value,
       * or 0 if not present.
       * <p/>
       * This method works just like {@link #getYears()} except
       * that this method works on the MONTHS field.
       *
       * @return Months of this <code>Duration</code>.
       */
      public int getMonths() {
          return getField(DatatypeConstants.MONTHS).intValue();
      }
  
      /**
       * Obtains the value of the DAYS field as an integer value,
       * or 0 if not present.
       * <p/>
       * This method works just like {@link #getYears()} except
       * that this method works on the DAYS field.
       *
       * @return Days of this <code>Duration</code>.
       */
      public int getDays() {
          return getField(DatatypeConstants.DAYS).intValue();
      }
  
      /**
       * Obtains the value of the HOURS field as an integer value,
       * or 0 if not present.
       * <p/>
       * This method works just like {@link #getYears()} except
       * that this method works on the HOURS field.
       *
       * @return Hours of this <code>Duration</code>.
       */
      public int getHours() {
          return getField(DatatypeConstants.HOURS).intValue();
      }
  
      /**
       * Obtains the value of the MINUTES field as an integer value,
       * or 0 if not present.
       * <p/>
       * This method works just like {@link #getYears()} except
       * that this method works on the MINUTES field.
       *
       * @return Minutes of this <code>Duration</code>.
       */
      public int getMinutes() {
          return getField(DatatypeConstants.MINUTES).intValue();
      }
  
      /**
       * Obtains the value of the SECONDS field as an integer value,
       * or 0 if not present.
       * <p/>
       * This method works just like {@link #getYears()} except
       * that this method works on the SECONDS field.
       *
       * @return seconds in the integer value. The fraction of seconds
       * will be discarded (for example, if the actual value is 2.5,
       * this method returns 2)
       */
      public int getSeconds() {
          return getField(DatatypeConstants.SECONDS).intValue();
      }
  
      /**
       * <p>Returns the length of the duration in milli-seconds.</p>
       * <p/>
       * <p>If the seconds field carries more digits than milli-second order,
       * those will be simply discarded (or in other words, rounded to zero.)
       * For example, for any Calendar value <code>x</code>,</p>
       * <pre>
       * <code>new Duration("PT10.00099S").getTimeInMills(x) == 10000</code>.
       * <code>new Duration("-PT10.00099S").getTimeInMills(x) == -10000</code>.
       * </pre>
       * <p/>
       * <p/>
       * Note that this method uses the {@link #addTo(Calendar)} method,
       * which may work incorrectly with <code>Duration</code> objects with
       * very large values in its fields. See the {@link #addTo(Calendar)}
       * method for details.
       *
       * @param startInstant The length of a month/year varies. The <code>startInstant</code> is
       *                     used to disambiguate this variance. Specifically, this method
       *                     returns the difference between <code>startInstant</code> and
       *                     <code>startInstant+duration</code>
       * @return milliseconds between <code>startInstant</code> and
       * <code>startInstant</code> plus this <code>Duration</code>
       * @throws NullPointerException if <code>startInstant</code> parameter
       *                              is null.
       */
      public long getTimeInMillis(final Calendar startInstant) {
          Calendar cal = (Calendar) startInstant.clone();
          addTo(cal);
          return getCalendarTimeInMillis(cal)
                  - getCalendarTimeInMillis(startInstant);
      }
  
      /**
       * <p>Returns the length of the duration in milli-seconds.</p>
       * <p/>
       * <p>If the seconds field carries more digits than milli-second order,
       * those will be simply discarded (or in other words, rounded to zero.)
       * For example, for any <code>Date</code> value <code>x</code>,</p>
       * <pre>
       * <code>new Duration("PT10.00099S").getTimeInMills(x) == 10000</code>.
       * <code>new Duration("-PT10.00099S").getTimeInMills(x) == -10000</code>.
       * </pre>
       * <p/>
       * <p/>
       * Note that this method uses the {@link #addTo(Date)} method,
       * which may work incorrectly with <code>Duration</code> objects with
       * very large values in its fields. See the {@link #addTo(Date)}
       * method for details.
       *
       * @param startInstant The length of a month/year varies. The <code>startInstant</code> is
       *                     used to disambiguate this variance. Specifically, this method
       *                     returns the difference between <code>startInstant</code> and
       *                     <code>startInstant+duration</code>.
       * @return milliseconds between <code>startInstant</code> and
       * <code>startInstant</code> plus this <code>Duration</code>
       * @throws NullPointerException If the startInstant parameter is null.
       * @see #getTimeInMillis(Calendar)
       */
      public long getTimeInMillis(final Date startInstant) {
          Calendar cal = new GregorianCalendar();
          cal.setTime(startInstant);
          this.addTo(cal);
          return getCalendarTimeInMillis(cal) - startInstant.getTime();
      }
  
      /**
       * Gets the value of a field.
       * <p/>
       * Fields of a duration object may contain arbitrary large value.
       * Therefore this method is designed to return a {@link Number} object.
       * <p/>
       * In case of YEARS, MONTHS, DAYS, HOURS, and MINUTES, the returned
       * number will be a non-negative integer. In case of seconds,
       * the returned number may be a non-negative decimal value.
       *
       * @param field one of the six Field constants (YEARS,MONTHS,DAYS,HOURS,
       *              MINUTES, or SECONDS.)
       * @return If the specified field is present, this method returns
       * a non-null non-negative {@link Number} object that
       * represents its value. If it is not present, return null.
       * For YEARS, MONTHS, DAYS, HOURS, and MINUTES, this method
       * returns a {@link java.math.BigInteger} object. For SECONDS, this
       * method returns a {@link java.math.BigDecimal}.
       * @throws NullPointerException If the <code>field</code> is <code>null</code>.
       */
      public abstract Number getField(final DatatypeConstants.Field field);
  
      /**
       * Checks if a field is set.
       * <p/>
       * A field of a duration object may or may not be present.
       * This method can be used to test if a field is present.
       *
       * @param field one of the six Field constants (YEARS,MONTHS,DAYS,HOURS,
       *              MINUTES, or SECONDS.)
       * @return true if the field is present. false if not.
       * @throws NullPointerException If the field parameter is null.
       */
      public abstract boolean isSet(final DatatypeConstants.Field field);
  
      /**
       * <p>Computes a new duration whose value is <code>this+rhs</code>.</p>
       * <p/>
       * <p>For example,</p>
       * <pre>
       * "1 day" + "-3 days" = "-2 days"
       * "1 year" + "1 day" = "1 year and 1 day"
       * "-(1 hour,50 minutes)" + "-20 minutes" = "-(1 hours,70 minutes)"
       * "15 hours" + "-3 days" = "-(2 days,9 hours)"
       * "1 year" + "-1 day" = IllegalStateException
       * </pre>
       * <p/>
       * <p>Since there's no way to meaningfully subtract 1 day from 1 month,
       * there are cases where the operation fails in
       * {@link IllegalStateException}.</p>
       * <p/>
       * <p>
       * Formally, the computation is defined as follows.</p>
       * <p>
       * Firstly, we can assume that two <code>Duration</code>s to be added
       * are both positive without losing generality (i.e.,
       * <code>(-X)+Y=Y-X</code>, <code>X+(-Y)=X-Y</code>,
       * <code>(-X)+(-Y)=-(X+Y)</code>)
       * <p/>
       * <p>
       * Addition of two positive <code>Duration</code>s are simply defined as
       * field by field addition where missing fields are treated as 0.
       * <p>
       * A field of the resulting <code>Duration</code> will be unset if and
       * only if respective fields of two input <code>Duration</code>s are unset.
       * <p>
       * Note that <code>lhs.add(rhs)</code> will be always successful if
       * <code>lhs.signum()*rhs.signum()!=-1</code> or both of them are
       * normalized.</p>
       *
       * @param rhs <code>Duration</code> to add to this <code>Duration</code>
       * @return non-null valid Duration object.
       * @throws NullPointerException  If the rhs parameter is null.
       * @throws IllegalStateException If two durations cannot be meaningfully added. For
       *                               example, adding negative one day to one month causes
       *                               this exception.
       * @see #subtract(Duration)
       */
      public abstract Duration add(final Duration rhs);
  
      /**
       * Adds this duration to a {@link Calendar} object.
       * <p/>
       * <p>
       * Calls {@link java.util.Calendar#add(int, int)} in the
       * order of YEARS, MONTHS, DAYS, HOURS, MINUTES, SECONDS, and MILLISECONDS
       * if those fields are present. Because the {@link Calendar} class
       * uses int to hold values, there are cases where this method
       * won't work correctly (for example if values of fields
       * exceed the range of int.)
       * </p>
       * <p/>
       * <p>
       * Also, since this duration class is a Gregorian duration, this
       * method will not work correctly if the given {@link Calendar}
       * object is based on some other calendar systems.
       * </p>
       * <p/>
       * <p>
       * Any fractional parts of this <code>Duration</code> object
       * beyond milliseconds will be simply ignored. For example, if
       * this duration is "P1.23456S", then 1 is added to SECONDS,
       * 234 is added to MILLISECONDS, and the rest will be unused.
       * </p>
       * <p/>
       * <p/>
       * Note that because {@link Calendar#add(int, int)} is using
       * <code>int</code>, <code>Duration</code> with values beyond the
       * range of <code>int</code> in its fields
       * will cause overflow/underflow to the given {@link Calendar}.
       * {@link XMLGregorianCalendar#add(Duration)} provides the same
       * basic operation as this method while avoiding
       * the overflow/underflow issues.
       *
       * @param calendar A calendar object whose value will be modified.
       * @throws NullPointerException if the calendar parameter is null.
       */
      public abstract void addTo(Calendar calendar);
  
      /**
       * Adds this duration to a {@link Date} object.
       * <p/>
       * <p/>
       * The given date is first converted into
       * a {@link java.util.GregorianCalendar}, then the duration
       * is added exactly like the {@link #addTo(Calendar)} method.
       * <p/>
       * <p/>
       * The updated time instant is then converted back into a
       * {@link Date} object and used to update the given {@link Date} object.
       * <p/>
       * <p/>
       * This somewhat redundant computation is necessary to unambiguously
       * determine the duration of months and years.
       *
       * @param date A date object whose value will be modified.
       * @throws NullPointerException if the date parameter is null.
       */
      public void addTo(Date date) {
  
          // check data parameter
          if (date == null) {
              throw new NullPointerException(
                      "Cannot call "
                              + this.getClass().getName()
                              + "#addTo(Date date) with date == null."
              );
          }
  
          Calendar cal = new GregorianCalendar();
          cal.setTime(date);
          this.addTo(cal);
          date.setTime(getCalendarTimeInMillis(cal));
      }
  
      /**
       * <p>Computes a new duration whose value is <code>this-rhs</code>.</p>
       * <p/>
       * <p>For example:</p>
       * <pre>
       * "1 day" - "-3 days" = "4 days"
       * "1 year" - "1 day" = IllegalStateException
       * "-(1 hour,50 minutes)" - "-20 minutes" = "-(1hours,30 minutes)"
       * "15 hours" - "-3 days" = "3 days and 15 hours"
       * "1 year" - "-1 day" = "1 year and 1 day"
       * </pre>
       * <p/>
       * <p>Since there's no way to meaningfully subtract 1 day from 1 month,
       * there are cases where the operation fails in {@link IllegalStateException}.</p>
       * <p/>
       * <p>Formally the computation is defined as follows.
       * First, we can assume that two <code>Duration</code>s are both positive
       * without losing generality.  (i.e.,
       * <code>(-X)-Y=-(X+Y)</code>, <code>X-(-Y)=X+Y</code>,
       * <code>(-X)-(-Y)=-(X-Y)</code>)</p>
       * <p/>
       * <p>Then two durations are subtracted field by field.
       * If the sign of any non-zero field <code>F</code> is different from
       * the sign of the most significant field,
       * 1 (if <code>F</code> is negative) or -1 (otherwise)
       * will be borrowed from the next bigger unit of <code>F</code>.</p>
       * <p/>
       * <p>This process is repeated until all the non-zero fields have
       * the same sign.</p>
       * <p/>
       * <p>If a borrow occurs in the days field (in other words, if
       * the computation needs to borrow 1 or -1 month to compensate
       * days), then the computation fails by throwing an
       * {@link IllegalStateException}.</p>
       *
       * @param rhs <code>Duration</code> to subtract from this <code>Duration</code>.
       * @return New <code>Duration</code> created from subtracting <code>rhs</code> from this <code>Duration</code>.
       * @throws IllegalStateException If two durations cannot be meaningfully subtracted. For
       *                               example, subtracting one day from one month causes
       *                               this exception.
       * @throws NullPointerException  If the rhs parameter is null.
       * @see #add(Duration)
       */
      public Duration subtract(final Duration rhs) {
          return add(rhs.negate());
      }
  
      /**
       * <p>Computes a new duration whose value is <code>factor</code> times
       * longer than the value of this duration.</p>
       * <p/>
       * <p>This method is provided for the convenience.
       * It is functionally equivalent to the following code:</p>
       * <pre>
       * multiply(new BigDecimal(String.valueOf(factor)))
       * </pre>
       *
       * @param factor Factor times longer of new <code>Duration</code> to create.
       * @return New <code>Duration</code> that is <code>factor</code>times longer than this <code>Duration</code>.
       * @see #multiply(BigDecimal)
       */
      public Duration multiply(int factor) {
          return multiply(new BigDecimal(String.valueOf(factor)));
      }
  
      /**
       * Computes a new duration whose value is <code>factor</code> times
       * longer than the value of this duration.
       * <p/>
       * <p>
       * For example,
       * <pre>
       * "P1M" (1 month) * "12" = "P12M" (12 months)
       * "PT1M" (1 min) * "0.3" = "PT18S" (18 seconds)
       * "P1M" (1 month) * "1.5" = IllegalStateException
       * </pre>
       * <p/>
       * <p>
       * Since the <code>Duration</code> class is immutable, this method
       * doesn't change the value of this object. It simply computes
       * a new Duration object and returns it.
       * <p/>
       * <p>
       * The operation will be performed field by field with the precision
       * of {@link BigDecimal}. Since all the fields except seconds are
       * restricted to hold integers,
       * any fraction produced by the computation will be
       * carried down toward the next lower unit. For example,
       * if you multiply "P1D" (1 day) with "0.5", then it will be 0.5 day,
       * which will be carried down to "PT12H" (12 hours).
       * When fractions of month cannot be meaningfully carried down
       * to days, or year to months, this will cause an
       * {@link IllegalStateException} to be thrown.
       * For example if you multiple one month by 0.5.</p>
       * <p/>
       * <p/>
       * To avoid {@link IllegalStateException}, use
       * the {@link #normalizeWith(Calendar)} method to remove the years
       * and months fields.
       *
       * @param factor to multiply by
       * @return returns a non-null valid <code>Duration</code> object
       * @throws IllegalStateException if operation produces fraction in
       *                               the months field.
       * @throws NullPointerException  if the <code>factor</code> parameter is
       *                               <code>null</code>.
       */
      public abstract Duration multiply(final BigDecimal factor);
  
      /**
       * Returns a new <code>Duration</code> object whose
       * value is <code>-this</code>.
       * <p/>
       * <p/>
       * Since the <code>Duration</code> class is immutable, this method
       * doesn't change the value of this object. It simply computes
       * a new Duration object and returns it.
       *
       * @return always return a non-null valid <code>Duration</code> object.
       */
      public abstract Duration negate();
  
      /**
       * <p>Converts the years and months fields into the days field
       * by using a specific time instant as the reference point.</p>
       * <p/>
       * <p>For example, duration of one month normalizes to 31 days
       * given the start time instance "July 8th 2003, 17:40:32".</p>
       * <p/>
       * <p>Formally, the computation is done as follows:</p>
       * <ol>
       * <li>the given Calendar object is cloned</li>
       * <li>the years, months and days fields will be added to the {@link Calendar} object
       * by using the {@link Calendar#add(int, int)} method</li>
       * <li>the difference between the two Calendars in computed in milliseconds and converted to days,
       * if a remainder occurs due to Daylight Savings Time, it is discarded</li>
       * <li>the computed days, along with the hours, minutes and seconds
       * fields of this duration object is used to construct a new
       * Duration object.</li>
       * </ol>
       * <p/>
       * <p>Note that since the Calendar class uses <code>int</code> to
       * hold the value of year and month, this method may produce
       * an unexpected result if this duration object holds
       * a very large value in the years or months fields.</p>
       *
       * @param startTimeInstant <code>Calendar</code> reference point.
       * @return <code>Duration</code> of years and months of this <code>Duration</code> as days.
       * @throws NullPointerException If the startTimeInstant parameter is null.
       */
      public abstract Duration normalizeWith(final Calendar startTimeInstant);
  
      /**
       * <p>Partial order relation comparison with this <code>Duration</code> instance.</p>
       * <p/>
       * <p>Comparison result must be in accordance with
       * <a href="http://www.w3.org/TR/xmlschema-2/#duration-order">W3C XML Schema 1.0 Part 2, Section 3.2.7.6.2,
       * <i>Order relation on duration</i></a>.</p>
       * <p/>
       * <p>Return:</p>
       * <ul>
       * <li>{@link DatatypeConstants#LESSER} if this <code>Duration</code> is shorter than <code>duration</code> parameter</li>
       * <li>{@link DatatypeConstants#EQUAL} if this <code>Duration</code> is equal to <code>duration</code> parameter</li>
       * <li>{@link DatatypeConstants#GREATER} if this <code>Duration</code> is longer than <code>duration</code> parameter</li>
       * <li>{@link DatatypeConstants#INDETERMINATE} if a conclusive partial order relation cannot be determined</li>
       * </ul>
       *
       * @param duration to compare
       * @return the relationship between <code>this</code> <code>Duration</code>and <code>duration</code> parameter as
       * {@link DatatypeConstants#LESSER}, {@link DatatypeConstants#EQUAL}, {@link DatatypeConstants#GREATER}
       * or {@link DatatypeConstants#INDETERMINATE}.
       * @throws UnsupportedOperationException If the underlying implementation
       *                                       cannot reasonably process the request, e.g. W3C XML Schema allows for
       *                                       arbitrarily large/small/precise values, the request may be beyond the
       *                                       implementations capability.
       * @throws NullPointerException          if <code>duration</code> is <code>null</code>.
       * @see #isShorterThan(Duration)
       * @see #isLongerThan(Duration)
       */
      public abstract int compare(final Duration duration);
  
      /**
       * <p>Checks if this duration object is strictly longer than
       * another <code>Duration</code> object.</p>
       * <p/>
       * <p>Duration X is "longer" than Y if and only if X>Y
       * as defined in the section 3.2.6.2 of the XML Schema 1.0
       * specification.</p>
       * <p/>
       * <p>For example, "P1D" (one day) > "PT12H" (12 hours) and
       * "P2Y" (two years) > "P23M" (23 months).</p>
       *
       * @param duration <code>Duration</code> to test this <code>Duration</code> against.
       * @return true if the duration represented by this object
       * is longer than the given duration. false otherwise.
       * @throws UnsupportedOperationException If the underlying implementation
       *                                       cannot reasonably process the request, e.g. W3C XML Schema allows for
       *                                       arbitrarily large/small/precise values, the request may be beyond the
       *                                       implementations capability.
       * @throws NullPointerException          If <code>duration</code> is null.
       * @see #isShorterThan(Duration)
       * @see #compare(Duration duration)
       */
      public boolean isLongerThan(final Duration duration) {
          return compare(duration) == DatatypeConstants.GREATER;
      }
  
      /**
       * <p>Checks if this duration object is strictly shorter than
       * another <code>Duration</code> object.</p>
       *
       * @param duration <code>Duration</code> to test this <code>Duration</code> against.
       * @return <code>true</code> if <code>duration</code> parameter is shorter than this <code>Duration</code>,
       * else <code>false</code>.
       * @throws UnsupportedOperationException If the underlying implementation
       *                                       cannot reasonably process the request, e.g. W3C XML Schema allows for
       *                                       arbitrarily large/small/precise values, the request may be beyond the
       *                                       implementations capability.
       * @throws NullPointerException          if <code>duration</code> is null.
       * @see #isLongerThan(Duration duration)
       * @see #compare(Duration duration)
       */
      public boolean isShorterThan(final Duration duration) {
          return compare(duration) == DatatypeConstants.LESSER;
      }
  
      /**
       * <p>Checks if this duration object has the same duration
       * as another <code>Duration</code> object.</p>
       * <p/>
       * <p>For example, "P1D" (1 day) is equal to "PT24H" (24 hours).</p>
       * <p/>
       * <p>Duration X is equal to Y if and only if time instant
       * t+X and t+Y are the same for all the test time instants
       * specified in the section 3.2.6.2 of the XML Schema 1.0
       * specification.</p>
       * <p/>
       * <p>Note that there are cases where two <code>Duration</code>s are
       * "incomparable" to each other, like one month and 30 days.
       * For example,</p>
       * <pre>
       * !new Duration("P1M").isShorterThan(new Duration("P30D"))
       * !new Duration("P1M").isLongerThan(new Duration("P30D"))
       * !new Duration("P1M").equals(new Duration("P30D"))
       * </pre>
       *
       * @param duration The object to compare this <code>Duration</code> against.
       * @return <code>true</code> if this duration is the same length as
       * <code>duration</code>.
       * <code>false</code> if <code>duration</code> is <code>null</code>,
       * is not a
       * <code>Duration</code> object,
       * or its length is different from this duration.
       * @throws UnsupportedOperationException If the underlying implementation
       *                                       cannot reasonably process the request, e.g. W3C XML Schema allows for
       *                                       arbitrarily large/small/precise values, the request may be beyond the
       *                                       implementations capability.
       * @see #compare(Duration duration)
       */
      @Override
      public boolean equals(final Object duration) {
  
          if (duration == null || !(duration instanceof Duration)) {
              return false;
          }
  
          return compare((Duration) duration) == DatatypeConstants.EQUAL;
      }
  
      /**
       * Returns a hash code consistent with the definition of the equals method.
       *
       * @see Object#hashCode()
       */
      @Override
      public abstract int hashCode();
  
      /**
       * <p>Returns a <code>String</code> representation of this <code>Duration</code> <code>Object</code>.</p>
       * <p/>
       * <p>The result is formatted according to the XML Schema 1.0 spec and can be always parsed back later into the
       * equivalent <code>Duration</code> <code>Object</code> by {@link DatatypeFactory#newDuration(String  lexicalRepresentation)}.</p>
       * <p/>
       * <p>Formally, the following holds for any <code>Duration</code>
       * <code>Object</code> x:</p>
       * <pre>
       * new Duration(x.toString()).equals(x)
       * </pre>
       *
       * @return A non-<code>null</code> valid <code>String</code> representation of this <code>Duration</code>.
       */
      @Override
      public String toString() {
  
          StringBuffer buf = new StringBuffer();
  
          if (getSign() < 0) {
              buf.append('-');
          }
          buf.append('P');
  
          BigInteger years = (BigInteger) getField(DatatypeConstants.YEARS);
          if (years != null) {
              buf.append(years + "Y");
          }
  
          BigInteger months = (BigInteger) getField(DatatypeConstants.MONTHS);
          if (months != null) {
              buf.append(months + "M");
          }
  
          BigInteger days = (BigInteger) getField(DatatypeConstants.DAYS);
          if (days != null) {
              buf.append(days + "D");
          }
  
          BigInteger hours = (BigInteger) getField(DatatypeConstants.HOURS);
          BigInteger minutes = (BigInteger) getField(DatatypeConstants.MINUTES);
          BigDecimal seconds = (BigDecimal) getField(DatatypeConstants.SECONDS);
          if (hours != null || minutes != null || seconds != null) {
              buf.append('T');
              if (hours != null) {
                  buf.append(hours + "H");
              }
              if (minutes != null) {
                  buf.append(minutes + "M");
              }
              if (seconds != null) {
                  buf.append(toString(seconds) + "S");
              }
          }
  
          return buf.toString();
      }
  
      /**
       * <p>Turns {@link BigDecimal} to a string representation.</p>
       * <p/>
       * <p>Due to a behavior change in the {@link BigDecimal#toString()}
       * method in JDK1.5, this had to be implemented here.</p>
       *
       * @param bd <code>BigDecimal</code> to format as a <code>String</code>
       * @return <code>String</code> representation of <code>BigDecimal</code>
       */
      private String toString(BigDecimal bd) {
          String intString = bd.unscaledValue().toString();
          int scale = bd.scale();
  
          if (scale == 0) {
              return intString;
          }
  
          /* Insert decimal point */
          StringBuffer buf;
          int insertionPoint = intString.length() - scale;
          if (insertionPoint == 0) { /* Point goes right before intVal */
              return "0." + intString;
          } else if (insertionPoint > 0) { /* Point goes inside intVal */
              buf = new StringBuffer(intString);
              buf.insert(insertionPoint, '.');
          } else { /* We must insert zeros between point and intVal */
              buf = new StringBuffer(3 - insertionPoint + intString.length());
              buf.append("0.");
              for (int i = 0; i < -insertionPoint; i++) {
                  buf.append('0');
              }
              buf.append(intString);
          }
          return buf.toString();
      }
  }
  