Can anyone explain why do I get those values while trying to parse a date?
I've tried three different inputs, as follows:
1) Third week of 2013
Date date = new SimpleDateFormat("ww.yyyy").parse("02.2013");
Calendar cal = Calendar.getInstance();
cal.setTime(date);
System.out.println(cal.get(Calendar.WEEK_OF_YEAR) + "." + cal.get(Calendar.YEAR));
Which outputs: 02.2013 (as I expected)
2) First week of 2013
Date date = new SimpleDateFormat("ww.yyyy").parse("00.2013");
Calendar cal = Calendar.getInstance();
cal.setTime(date);
System.out.println(cal.get(Calendar.WEEK_OF_YEAR) + "." + cal.get(Calendar.YEAR));
Which outputs: 52.2012 (which is fine for me, since the first week of 2013 is also the last one of 2012)
3) Second week of 2013
Date date = new SimpleDateFormat("ww.yyyy").parse("01.2013");
Calendar cal = Calendar.getInstance();
cal.setTime(date);
System.out.println(cal.get(Calendar.WEEK_OF_YEAR) + "." + cal.get(Calendar.YEAR));
Which outputs: 1.2012 (which makes absolutely no sense to me)
Does anyone know why this happens?? I need to parse a date in the format (week of year).(year). Am I using the wrong pattern?
You're using ww, which is "week of week-year", but then yyyy which is "calendar year" rather than "week year". Setting the week-of-week-year and then setting the calendar year is a recipe for problems, because they're just separate numbering systems, effectively.
You should be using YYYY in your format string to specify the week-year... although unfortunately it looks like you can't then get the value in a sane way. (I'd expect a Calendar.WEEKYEAR constant, but there is no such thing.)
Also, week-of-year values start at 1, not 0... and no week is in two week-years; it's either the first week of 2013 or it's the last week of 2012... it's not both.
I would personally avoid using week-years and weeks if you possibly can - they can be very confusing, particularly when a date in one calendar year is in a different week year.
Use Calendar.getWeekYear() to get year value synced with Calendar.WEEK_OF_YEAR field.
There is more information about Week of Year and Week Year at the GregorianCalendar doc.
Related
I'm trying to get the sunday of the same week as a given date.
During this I ran into this problem:
Calendar calendar = Calendar.getInstance(Locale.GERMANY);
calendar.set(2017, 11, 11);
calendar.set(Calendar.DAY_OF_WEEK, Calendar.SUNDAY);
System.out.println(calendar.getTime().toString());
results in "Sun Jan 07 11:18:42 CET 2018"
but
Calendar calendar2 = Calendar.getInstance(Locale.GERMANY);
calendar2.set(2017, 11, 11);
calendar2.getTime();
calendar2.set(Calendar.DAY_OF_WEEK, Calendar.SUNDAY);
System.out.println(calendar2.getTime().toString());
gives me the correct Date "Sun Dec 17 11:18:42 CET 2017"
Can someone explain why the first exmple is behaving this way? Is this really intended?
Thanks
Basically, the Calendar API is horrible, and should be avoided. It's not documented terribly clearly, but I think I see where it's going, and it's behaving as intended in this situation. By that I mean it's following the intention of the API authors, not the intention of you or anyone reading your code...
From the documentation:
The calendar field values can be set by calling the set methods. Any field values set in a Calendar will not be interpreted until it needs to calculate its time value (milliseconds from the Epoch) or values of the calendar fields. Calling the get, getTimeInMillis, getTime, add and roll involves such calculation.
And then:
When computing a date and time from the calendar fields, there may be insufficient information for the computation (such as only year and month with no day of month), or there may be inconsistent information (such as Tuesday, July 15, 1996 (Gregorian) -- July 15, 1996 is actually a Monday). Calendar will resolve calendar field values to determine the date and time in the following way.
If there is any conflict in calendar field values, Calendar gives priorities to calendar fields that have been set more recently. The following are the default combinations of the calendar fields. The most recent combination, as determined by the most recently set single field, will be used.
For the date fields:
YEAR + MONTH + DAY_OF_MONTH
YEAR + MONTH + WEEK_OF_MONTH + DAY_OF_WEEK
YEAR + MONTH + DAY_OF_WEEK_IN_MONTH + DAY_OF_WEEK
YEAR + DAY_OF_YEAR
YEAR + DAY_OF_WEEK + WEEK_OF_YEAR
In the first example, the fact that the last field set was "day of week" means it will then use the YEAR + MONTH + WEEK_OF_MONTH + DAY_OF_WEEK calculation (I think). The year and month have been set to December 2017, but the week-of-month is the current week-of-month, which is the week 5 of January 2018... so when you then say to set the day of week to Sunday, it's finding the Sunday in the "week 5" of December 2017. December only had 4 weeks, so it's effectively rolling it forward... I think. It's all messy and you shouldn't have to think about that, basically.
In the second example, calling getTime() "locks in" the year/month/day you've specified, and computes the other fields. When you set the day of week, that's then adjusting it within the existing computed fields.
Basically, avoid this API as far as you possibly can. Use java.time, which is a far cleaner date/time API.
As Jon Skeet said, avoid Calendar. For your case it is truly horrible, and it’s poorly designed in general. Instead do
WeekFields weekFieldsForLocale = WeekFields.of(Locale.GERMANY);
// To find out which number Sunday has in the locale,
// grab any Sunday and get its weekFieldsForLocale.dayOfWeek()
int dayNumberOfSundayInLocale = LocalDate.now()
.with(TemporalAdjusters.nextOrSame(DayOfWeek.SUNDAY))
.get(weekFieldsForLocale.dayOfWeek());
LocalDate date = LocalDate.of(2017, Month.DECEMBER, 11);
LocalDate sunday
= date.with(weekFieldsForLocale.dayOfWeek(), dayNumberOfSundayInLocale);
System.out.println(sunday);
This prints the expected date
2017-12-17
As others have already mentioned, the solution is to use java.time, the modern Java date and time API. Also generally it is so much nicer to work with. One nice feature is the LocalDate class that I am using. It is a date without time of day, which seems to match your requirements more precisely that Calendar did.
If the above looks complicated, it’s because, as I think you are aware, “Sunday of the same week” means different things in different locales. In the international standard that Germany follows, weeks begin on Monday, so Sunday is the last day of the week. In the American standard, for example, Sunday os the first day of the week. WeekFields.dayOfWeek() numbers the days of the week from 1 to 7, so when we want to set the day to Sunday, we first need to find out which number Sunday has got in this numbering (7 in Germany, 1 in the US). So for any Sunday, get its weekFieldsForLocale.dayOfWeek() value and later use this for setting the day of week to Sunday. The reason why this is necessary is that the with() method is so general and therefore has been designed to accept only numeric values; we can’t just pass it a DayOfWeek object.
If I substitute Locale.US into the code, I get 2017-12-10, which is the correct Sunday for a calendar where Sunday is the first day of the week. If you are sure your only want your code to work for Germany, you may of course just hardcode a 7 (please make it a constant with a very explanatory name).
Link: Oracle Tutorial Date Time explaining how to use java.time. There are other resources on the net (just avoid the outdated placed that suggest java.util.Calendar :-)
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Retrieve current week's Monday's date
(9 answers)
Closed 5 years ago.
In my case week start from Monday to Sunday.I want get current week Monday date.
I using following code to get Monday date.
Calendar c = Calendar.getInstance();
c.set(Calendar.DAY_OF_WEEK, Calendar.MONDAY);
System.out.println("Date " + c.getTime());
It works fine for all days except Sunday,If current day is Sunday it will give next week Monday date.Is it possible get current week Monday date using java.util.Date/Calendar API even if it is Sunday.
Any help appreciated.
You can tell the Calendar class what day of the week should be considered as the first one. Try adding the following line:
c.setFirstDayOfWeek(Calendar.MONDAY);
LocalDateTime thisWeeksMonday = LocalDateTime.now().with(DayOfWeek.MONDAY);
just in case that Java 8 is an option.
As stated in "Get date of first day of week based on LocalDate.now() in Java 8" your usage may differ.
Regarding Java <8 you need to set setFirstDayOfWeek as Jack mentioned. Just be sure that you set it before you alter your day of week, e.g.:
Calendar c = Calendar.getInstance();
c.setFirstDayOfWeek(Calendar.MONDAY);
c.set(Calendar.DAY_OF_WEEK, Calendar.MONDAY);
System.out.println("Date " + c.getTime());
Here's my code:
java.util.Date TODAY = new java.util.Date();
SimpleDateFormat SDF = new SimpleDateFormat( "YYYY-MM-DD" );
System.out.println ( SDF.format( TODAY ) );'
And the result is:
2015-02-33
But today's date is 2015-02-02!
What may be the reason behind this wrong output?
You want to use the yyyy year and dd day of the month.
However, I suggest you migrate to JSR-310 which is built into Java 8 and available for earlier versions of Java. The same code is
System.out.println(LocalDate.now());
prints
2105-02-02
What may be the reason behind this Wrong Output ?
Your assumptions about the date format string are wrong, the output is correct.
y Year
Y Week year
D Day in year
d Day in month
M Month in year
m Minute in hour
http://docs.oracle.com/javase/7/docs/api/java/text/SimpleDateFormat.html
Y Week year will usually give incorrect results around new year. D will give incorrect results from February. So your format appeared fine most of last month.
When format for SimpleDateFormat is specified as follows:
SimpleDateFormat sdf = new SimpleDateFormat("YYYY-MM-DD");
the YYYY - means week year,
the MM - means month,
the DD - means day in year.
Week year here is not what you wanted. See what is week year.
Your today's date is 2015-02-02, which means that it is 32 days since the beginning of the year 2015 passed and your are on the 33 day. That is why you get date "2015-02-33".
To mean year (and not week year) and day in month change format to SimpleDateFormat("yyyy-MM-dd");
I have the following code in a JUnit test, which seemed to work last week is failing this week:
Calendar cal = Calendar.getInstance();
cal.set(2011, Calendar.JULY, 12);
cal.set(Calendar.DAY_OF_WEEK, Calendar.FRIDAY); // push the date to 15
System.out.println(cal.get(Calendar.DATE));
As you could probably infer from my comment, since the 12th is a Tuesday, I expect Date to be 15 after setting the DAY_OF_WEEK to Friday. However, the value that is printed is 22, and causes the test to fail.
If I, however change the code as follows, and add an additional call to get:
Calendar cal = Calendar.getInstance();
cal.set(2011, Calendar.JULY, 12);
System.out.println(cal.get(Calendar.DATE));
cal.set(Calendar.DAY_OF_WEEK, Calendar.FRIDAY); // push the date to 15
System.out.println(cal.get(Calendar.DATE));
I get the output that I expect, 12 and 15.
Can someone explain what is going on, and why this test was working last week?
The first thing to understand is that Month + Day + DayOfWeek does not mean anything to the Calendar. The Calendar will calculate the true value of the date based on
YEAR + MONTH + DATE
or
YEAR + MONTH + WEEK_OF_MONTH + DAY_OF_WEEK
(Or some other combos like year + day of year etc.) So Date + DayOfWeek doesn't inherently mean much to it.
The second thing to understand is when you set on a Java Calendar it doesn't actually recompute the absolute time or update related fields until an operation that forces computation occurs.
After your first set, the calendar is in a conflicted state. The month and day say that it's July 12th, but the 'week of month' and 'day of week' still say that it's today, whatever today is. You then call set day of week to friday. So now year month and day say July 12th, but the 'week of month' and 'day of week' fields say it's Friday of 'this' week.
The rules of the calendar say that the most recently set field "wins" when there's a conflict, so the week of month and day of week combining to say Friday of this week are what's used to calculate the other fields.
Inserting a get in the middle 'fixes' it because it forces the entire internal state of the calendar to get recomputed to Tuesday July 12th before setting to Friday, so there are no internal conflicts. The 'week of month' got set to the week that contains July 12th by the recalculation prior to you setting day of week to Friday.
Edit: Sorry to make changes after two days, noticed this open in an old browser tab and thought I would expand for the hopeful help of future googlers:
The reason it worked for Jon in the comments is he lives in London. His computer thinks weeks start on Mondays. So when asked for Friday of 'this' week, it still responded July 15th when asked on Sunday July 17th. I bring this up because differing first days of the week in different Locales are just yet another way that trying to use the WEEK_OF fields in a calendar goes haywire.
There is Bug 4655637 (looks similar to your issue). I checked that code under latest JDK6 (Windows) and I have 15 in both cases. BTW: I am suggest to always use GregorianCalendar class explicitly unless you want something else (depending on your locale).
EDIT: official docs:
The following are the default combinations of the calendar fields. The
most recent combination, as determined by the most recently set single
field, will be used.
For the date fields:
YEAR + MONTH + DAY_OF_MONTH
YEAR + MONTH + WEEK_OF_MONTH + DAY_OF_WEEK
YEAR + MONTH + DAY_OF_WEEK_IN_MONTH + DAY_OF_WEEK
YEAR + DAY_OF_YEAR
YEAR + DAY_OF_WEEK + WEEK_OF_YEAR
For the time of day fields:
HOUR_OF_DAY
AM_PM + HOUR
In addition to #Affe's clear answer, the following combinations seem to work (as of #GrzegorzSzpetkowski's bug report link)
Calendar expects the following combinations of the fields to determine
a date.
MONTH + DAY_OF_MONTH
MONTH + WEEK_OF_MONTH + DAY_OF_WEEK
MONTH + DAY_OF_WEEK_IN_MONTH + DAY_OF_WEEK
DAY_OF_YEAR
DAY_OF_WEEK + WEEK_OF_YEAR
When you set DAY_OF_WEEK, the calendar expects a week field
(WEEK_OF_MONTH, DAY_OF_WEEK_IN_MONTH or WEEK_OF_YEAR) has also been
set. So, avoid setting DAY_OF_WEEK without setting one of the week
fields.
This question already has answers here:
Closed 11 years ago.
Possible Duplicate:
How to subtract 45 days from from the current sysdate
Hi I am getting the current system date by using
Java.util.Date date = new java.util.Date();
How can i check whether my Date is One month Before date
For example if today is May 22 2011
How can i check if the date is of April 22 2011 ??
You could use JodaTime. Its DateTime class has a minusMonth-method. Use this to get the date from one month ago and then compare. See the Joda-API for more details.
Calendar cal1 = Calendar.getInstance();
cal1.setTime(theGivenDate);
Calendar cal2 = Calendar.getInstance();
cal2.add(Calendar.MONTH, -1);
if ( (cal1.get(Calendar.YEAR) == cal2.get(Calendar.YEAR)) &&
(cal1.get(Calendar.MONTH) == cal2.get(Calendar.MONTH)) &&
(cal1.get(Calendar.DAY_OF_MONTH) == cal2.get(Calendar.DAY_OF_MONTH)) ) {
System.out.println("Given date "
+ theGivenDate + " is exactly one month ago from today");
}
You can use Joda DateTime [http://joda-time.sourceforge.net/apidocs/org/joda/time/DateTime.html] for this.
DateTime has a method minusMonths(int months), and then you can convert Joda DateTime to java.util.Date
Are you aware that many dates will never be "one month before today" according to your definition for month as "calendar month"? For example, since June has only 30 days, the condition will never be true for May 31st.
You may want to change your definition to that commonly used by banks for purposes like calculating interest and deposit terms: a month is considered to be exactly 30 days, independent of calendar dates. So "one month after" May 31st would be June 30th.