Date/Time/Number Formatting
Alan Liu
Globalization Center of Competency
IBM Emerging Technology Center
Cupertino, CA, USA / September, 2000
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First ICU DeveloperWorkshop
Overview
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The Problem
• Display a date in different languages
– English:
– German:
– French:
Cupertino, CA, USA / September, 2000
Friday, June 4, 1999
Freitag, 4. Juni 1999
vendredi 4 juin 1999
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The Problem
• Display a date in different languages
• Convert a time between local time zones
– Los Angeles: June 3, 1999 5:00 PM PDT
– New York: June 3, 1999 8:00 PM EDT
– Paris:
June 4, 1999 2:00 AM CEST
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The Problem
• Display a date in different languages
• Convert a time between local time zones
• Handle daylight savings time
– Sat. Oct. 28, 2000 3:00 PM PDT + 24 hours =
– Sun. Oct. 29, 2000 2:00 PM PST
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The Problem
• These problems boil down to:
– Formatting
– Parsing
– Data conversion
• These operations apply to different data types:
– Dates and times
– Numbers, including currency amounts
– Messages
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Formatting and Parsing
• Formatting = conversion of binary data to
text
• Parsing = conversion of text to binary data
• Different locales use different text to
represent the same piece of binary data
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Data Conversion
• In different locales, not only the form but
also the value of displayed data may
change
• Reflects different local conventions: time
zone, definition of the week, calendar
• Applies only to dates and times
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Data Conversion
• Displayed data values differ depending on
the locale
• Underlying binary data does not change
• Displayed data: Calendar fields
• Underlying data: UDate scalar
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Data Conversion
• Conversion happens implicitly during
formatting and parsing
• Conversion can also be done explicitly
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Date and Time
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Date and Time
•
•
•
•
Date and time stored together as a scalar
Resolution of 1 millisecond
Range roughly 70,000 BC to 70,000 AD
Stored as absolute time independent of
local time zones (GMT-based)
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Date and Time
• Extensible calendar system
• Rule-based time zones with built-in data for
all modern international zones (over 400)
• Rule-based date format with built-in data
for many locales (over 140)
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Date and Time Components
•
•
•
•
UDate: GMT-based date and time (ms)
Calendar: Convert UDate to/from fields
TimeZone: Convert GMT to/from local zone
DateFormat: Convert UDate to/from text
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Date and Time Components
• Fit together in a specific nested pattern
DateFormat
Calendar
TimeZone
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Date and Time Components
•
Fit together in a specific nested pattern
1) Create
• TimeZone object zone
• Calendar object cal
• DateFormat object fmt
2) Set cal’s time zone to zone
3) Set fmt’s calendar to cal
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Date and Time Components
• If components are not nested explicitly,
then they use default objects, which can
lead to errors
• DateFormat uses a default
Calendar
• Calendar uses a default TimeZone
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Calendar: Two Roles
• Always set to a specific UDate
• Converts UDate to/from fields
– Fields are integer values for the month, day,
year, hour, minutes, day of week, etc.
– See calendar.h for complete field list
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Detail: Calendar Fields
• Conversion of fields to UDate
cal.clear();
cal.set(YEAR, 1999);
cal.set(MONTH, JUNE);
cal.set(DAY_OF_WEEK, MONDAY);
cal.set(WEEK_OF_MONTH, 2);
UDate d = cal.getTime();
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Detail: Calendar Fields
• Conversion of UDate to fields
cal.setTime(myUDate);
int32_t month = cal.get(MONTH);
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Time Zones
•
•
•
•
•
Standard Olson (UNIX) time zone data
Over 400 international time zones
Does not rely on host OS
No historical time zone support
Time zones always used with calendars
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Formatters: Code + Patterns
• Code contains generic pattern engine
• Locale resources contain different patterns
– Different groups of patterns for different locales
– Within each group, different patterns for different
variants; e.g., one for “Wed 6 Sep 00” and another
for “Wednesday 7 September 2000”
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Formatter: Types
• DateFormat already discussed
• NumberFormat handles “$1,234.56”
• MessageFormat handles “3 Files
Found”
• ChoiceFormat handles “no
files”/“one file”
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Formatters: Pattern Syntax
• Each formatter supports its own pattern syntax
• For number and date formats, most users can
use locale data
• For message format, users will have to write
their own patterns
• See headers for pattern syntax documentation
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Future Directions
• Support for time zone aliasing
• Support for traditional calendar systems
• Support for rule-based number
formatting (e.g., “three hundred and
sixty-four”)
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Exercises
• Exercise 1 – datefmt
– Use DateFormat to format a date and
time into several localized strings
– Convert the date and time into local time
zones
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Exercises
• Exercise 2 – msgfmt
– Use MessageFormat to format a number
and date
– Use a ChoiceFormat pattern to format
the number idiomatically
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