I have this code:
Calendar current = GregorianCalendar.getInstance(Locale.getDefault());
current.setFirstDayOfWeek(Calendar.MONDAY);
current.set(Calendar.DAY_OF_WEEK, Calendar.SUNDAY);
Today is Friday, Dec. 6. When I run it, I expect that the current week should be Monday, Dec 2->Sunday, Dec. 8, and current should now be set to Dec. 8. However, it is set to Dec. 1. Isn't that breaking the setFirstDayOfWeek call that I made?
LocalDate.now( ZoneId.of( "Africa/Tunis" ) ) // Get today’s date as seen by the people of a particular region (time zone).
.with( TemporalAdjusters.nextOrSame( DayOfWeek.MONDAY ) ) // Move to the next Monday, unless today is already a Monday.
You are using terribly troublesome old Calendar class that is now obsolete legacy, supplanted by the java.time classes.
LocalDateThe LocalDate class represents a date-only value without time-of-day and without time zone.
A time zone is crucial in determining a date. For any given moment, the date varies around the globe by zone. For example, a few minutes after midnight in Paris France is a new day while still “yesterday” in Montréal Québec.
If no time zone is specified, the JVM implicitly applies its current default time zone. That default may change at any moment, so your results may vary. Better to specify your desired/expected time zone explicitly as an argument.
Specify a proper time zone name in the format of continent/region, such as America/Montreal, Africa/Casablanca, or Pacific/Auckland. Never use the 3-4 letter abbreviation such as EST or IST as they are not true time zones, not standardized, and not even unique(!).
ZoneId z = ZoneId.of( "America/Montreal" ) ;
LocalDate today = LocalDate.now( z ) ;
If you want to use the JVM’s current default time zone, ask for it and pass as an argument. If omitted, the JVM’s current default is applied implicitly. Better to be explicit, as the default may be changed at any moment during runtime by any code in any thread of any app within the JVM.
ZoneId z = ZoneId.systemDefault() ; // Get JVM’s current default time zone.
Or specify a date. You may set the month by a number, with sane numbering 1-12 for January-December.
LocalDate ld = LocalDate.of( 1986 , 2 , 23 ) ; // Years use sane direct numbering (1986 means year 1986). Months use sane numbering, 1-12 for January-December.
Or, better, use the Month enum objects pre-defined, one for each month of the year. Tip: Use these Month objects throughout your codebase rather than a mere integer number to make your code more self-documenting, ensure valid values, and provide type-safety.
LocalDate ld = LocalDate.of( 1986 , Month.FEBRUARY , 23 ) ;
You can get the day-of-week represented as a DayOfWeek enum object.
DayOfWeek dow = ld.getDayOfWeek() ;
To move to another date, use a TemporalAdjuster implementation found in TemporalAdjusters class.
LocalDate nextOrSameMonday = ld.with( TemporalAdjusters.nextOrSame( DayOfWeek.MONDAY ) ) ;
The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date, Calendar, & SimpleDateFormat.
The Joda-Time project, now in maintenance mode, advises migration to the java.time classes.
To learn more, see the Oracle Tutorial. And search Stack Overflow for many examples and explanations. Specification is JSR 310.
Where to obtain the java.time classes?
The ThreeTen-Extra project extends java.time with additional classes. This project is a proving ground for possible future additions to java.time. You may find some useful classes here such as Interval, YearWeek, YearQuarter, and more.
The workaround for this has been to use JodaTime (of course). This works for me because JodaTime assumes that weeks start on Monday. Unfortunately, there is no way to change the day that JodaTime treats as the first day of the week.
DateTime dt = new DateTime();
dt = dt.withDayOfWeek(DateTimeConstants.SUNDAY);
Calendar current = dt.toGregorianCalendar();
