1. BPJ444: Dates Peter Liu Tim McKenna Seneca@York

2. Dates, Calendars, and what year is this? §Java tries to take an OOD approach to “when is now?” §import java.util.*; // get util package §Date class – represents a point in time §Calendar class – a general way to organize time §java.GregorianCalendar –a specific way to organize time.specific way to organize time

3. Date and Time ucurrent date and time (in milliseconds) after January 1, 1970 00:00:00 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!

4. GregorianCalendar uGregorianCalendar extends Calendar ucaptures ms timestamp and time zone u constructors can create current or other date u getTime( ) returns a Date object u get(Calendar.YEAR / MONTH / DATE / etc ) u set or add(Calendar.YEAR/etc, int ) u boolean gc1.after(gc2) or gc1.before(gc2) uExample: DateTime.java

5. GregorianCalendar caution §always follow one or more.set(Calendar.XXX) method calls with any.get(Calendar.XXX) call. §GregorianCalendar today = new GregorianCalendar(); // current date today.set(Calendar.HOUR_OF_DAY, 0); today.set(Calendar.MINUTE, 0); today.set(Calendar.SECOND, 0); today.get(Calendar.DATE); // update fields

6. GregorianCalendar alternative §see Joda-Time at http://joda-time.sourceforge.net/index.html http://joda-time.sourceforge.net/index.html §Stephen Colebourne is the Lead Technical Architect … see his presentation in a PDFStephen ColebournePDF §Joda-Time may be needed in applications that do a lot of date and time processing

7. Formatting Date and Time ujava.text.SimpleDateFormat - constructors - date formatting symbols - format( ) uonly works if set() was followed by get() uExample: FormatDateTime.java

8. Preset Formatters ujava.text.DateFormat - the parent class of SimpleDateFormat uDateFormat constants: SHORT, MEDIUM, LONG, FULL uDateFormat static methods : getDateInstance( ), getTimeInstance( ), getDateTimeInstance( ) retrieve normal format for that system uExample: DefaultFormats.java