Formats and parses date specification based on the
 draft-ietf-drums-msg-fmt-08 dated January 26, 2000.
 This is a followup spec to RFC822.
 
 This class does not take pattern strings.
 It always formats the date based on the specification below.
 
 3.3 Date and Time Specification
 
 Date and time occur in several header fields of a message. This section
 specifies the syntax for a full date and time specification. Though folding
 whitespace is permitted throughout the date-time specification, it is
 recommended that only a single space be used where FWS is required and 
 no space be used where FWS is optional in the date-time specification;
 some older implementations may not interpret other occurrences of folding 
 whitespace correctly.
 
date-time = [ day-of-week "," ] date FWS time [CFWS]
day-of-week = ([FWS] day-name) / obs-day-of-week
day-name = "Mon" / "Tue" / "Wed" / "Thu" / "Fri" / "Sat" / "Sun"
date = day month year
year = 4*DIGIT / obs-year
month = (FWS month-name FWS) / obs-month
month-name = "Jan" / "Feb" / "Mar" / "Apr" /
"May" / "Jun" / "Jul" / "Aug" /
"Sep" / "Oct" / "Nov" / "Dec"
day = ([FWS] 1*2DIGIT) / obs-day
time = time-of-day FWS zone
time-of-day = hour ":" minute [ ":" second ]
hour = 2DIGIT / obs-hour
minute = 2DIGIT / obs-minute
second = 2DIGIT / obs-second
zone = (( "+" / "-" ) 4DIGIT) / obs-zone
 
 The day is the numeric day of the month.
 The year is any numeric year in the common era.
 
 The time-of-day specifies the number of hours, minutes, and optionally 
 seconds since midnight of the date indicated.
 
 The date and time-of-day SHOULD express local time.
 
 The zone specifies the offset from Coordinated Universal Time(UTC,
 formerly referred to as "Greenwich Mean Time") that the date and 
 time-of-day represent.
 The "+" or "-" indicates whether the time-of-day is ahead of or behind
 Universal Time. The first two digits indicate the number of hours'
 difference from Universal Time, and the last two digits indicate the 
 number of minutes' difference from Universal Time.(Hence, +hhmm means 
 +(hh * 60 + mm) minutes, and -hhmm means -(hh * 60 + mm) minutes).
 The form "+0000" SHOULD be used to indicate a time zone at Universal Time.
 Though "-0000" also indicates Universal Time, it is used to indicate that 
 the time was generated on a system that may be in a local time zone other 
 than Universal Time.
 
 A date-time specification MUST be semantically valid.
 That is, the day-of-the week(if included) MUST be the day implied by 
 the date, the numeric day-of-month MUST be between 1 and the number of 
 days allowed for the specified month(in the specified year), the 
 time-of-day MUST be in the range 00:00:00 through 23:59:60(the number 
 of seconds allowing for a leap second; see [STD-12]), and the zone MUST 
 be within the range -9959 through +9959.
format
public StringBuffer format(Date date,
                           StringBuffer buf,
                           FieldPosition field) Appends the textual value for the specified field to the given string
 buffer. This method should be avoided, use format(Date)
 instead.
- date- the Date object
- buf- the buffer to append to
- field- the current field position
- the modified buffer
parse
public Date parse(String text,
                  ParsePosition pos) Parses the given date in the format specified by
 draft-ietf-drums-msg-fmt-08 in the current TimeZone.
- text- the formatted date to be parsed
- pos- the current parse position
setCalendar
public void setCalendar(Calendar newCalendar)
 Don't allow setting the calendar.
setNumberFormat
public void setNumberFormat(NumberFormat newNumberFormat)
 Don't allow setting the NumberFormat.