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Date and Time ucurrent date and time (in milliseconds) after January 1, :00:00 GMT u long ms = System.currentTimeMillis( ) umilliseconds as a date & time object u java.util.Date date = new Date(); uDate is mostly deprecated because… uis a Date created at this moment here the same as one created in Australia? same ms but different date/time to us uDate assumes local time zone!
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BPJ444: Dates Peter Liu
Tim McKennaSeneca@York
Dates, Calendars, and what year is this?Java tries to take an OOD approach to
“when is now?”import java.util.*; // get util packageDate class – represents a point in timeCalendar class – a general way to
organize timejava.GregorianCalendar –a
specific way to organize time.
Date and Time current date and time (in milliseconds)
after January 1, 1970 00:00:00 GMT long ms = System.currentTimeMillis( )
milliseconds as a date & time object java.util.Date date = new Date();
Date is mostly deprecated because… is a Date created at this moment here
the same as one created in Australia? same ms but different date/time to us
Date assumes local time zone!
GregorianCalendar GregorianCalendar extends Calendar captures ms timestamp and time zone
constructors can create current or other date getTime( ) returns a Date object get(Calendar.YEAR / MONTH / DATE / etc ) set or add(Calendar.YEAR/etc , int ) boolean gc1.after(gc2) or gc1.before(gc2)
Example: DateTime.java
GregorianCalendar cautionalways follow one or more
.set(Calendar.XXX) method calls with any .get(Calendar.XXX) call.
GregorianCalendar today = new GregorianCalendar(); // current datetoday.set(Calendar.HOUR_OF_DAY, 0);today.set(Calendar.MINUTE, 0);today.set(Calendar.SECOND, 0);today.get(Calendar.DATE); // update fields
GregorianCalendar alternative
see Joda-Time at http://joda-time.sourceforge.net/index.html
Stephen Colebourne is the Lead Technical Architect … see his presentation in a PDF
Joda-Time may be needed in applications that do a lot of date and time processing
Formatting Date and Time java.text.SimpleDateFormat
- constructors - date formatting
symbols - format( ) only works if set() was followed by
get() Example: FormatDateTime.java
Preset Formatters java.text.DateFormat - the parent class
of SimpleDateFormat DateFormat constants: SHORT,
MEDIUM, LONG, FULL DateFormat static methods :
getDateInstance( ), getTimeInstance( ), getDateTimeInstance( )
retrieve normal format for that system Example: DefaultFormats.java
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