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Get Date in Java given Week number, week day and year

Given Week of the year, the week day and the year, how can we get the Date in Java?
With Jodatime, I tried the following:
DateTime dt = new DateTime();
dt.withYear(year);
dt.withWeekOfWeekyear(weekOfYear);
dt.withDayOfWeek(weekDay);
DateTimeFormatter dateTimeFormatter = DateTimeFormat.forPattern("yyMMdd");
System.out.println(dateTimeFormatter.print(dt));
But it gets the current Date!

JodaTime returns a changed copy, so do:
DateTime dt = new DateTime()
.withWeekyear(year)
.withWeekOfWeekyear(weekOfYear)
.withDayOfWeek(weekDay);
DateTimeFormatter dateTimeFormatter = DateTimeFormat.forPattern("yyMMdd");
System.out.println(dateTimeFormatter.print(dt));
And this should work as expected.

The accepted answer has bug..withYear(year) should be withWeekyear(year). #Neet please update it.

You need to reassign the date afterwards!
the dt.with*() methods simply make a copy of the date.
try
DateTime dt = new DateTime();
dt = dt.withYear(year);
dt = dt.withWeekOfWeekyear(weekOfYear);
dt = dt.withDayOfWeek(weekDay);
DateTimeFormatter dateTimeFormatter = DateTimeFormat.forPattern("yyMMdd");
System.out.println(dateTimeFormatter.print(dt));

We can also use this native java code using Calendar class:
SimpleDateFormat sdf = new SimpleDateFormat("MM dd yyyy");
Calendar cal = Calendar.getInstance();
cal.set(Calendar.WEEK_OF_YEAR, 23);
cal.set(Calendar.DAY_OF_WEEK, 3);
cal.set(Calendar.YEAR,2013);
System.out.println(sdf.format(cal.getTime()));

Here is a simple example of how to do it without JodaTime:
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
public class Snippet {
public static void main(String args[]) {
String year = "2013";
String week_of_year = "46";
String day_of_week = "4";
String yearweekday = year + week_of_year + day_of_week;
SimpleDateFormat sdf = new SimpleDateFormat("yyyywwu");
Date date = null;
try {
date = sdf.parse(yearweekday);
} catch (ParseException e) {
e.printStackTrace();
}
System.out.println(date);
}
}
Good luck!

tl;dr
YearWeek.of( 2017 , 1 )
.atDay( DayOfWeek.TUESDAY )
.format( DateTimeFormatter.ofPattern( "uuMMdd" ) )
“Week” ambiguous
The word 'week' is ambiguous. Do you mean week number 1 contains January 1? Or week number 1 contains the first of a particular day of year such as Sunday or Monday?
Or do you mean a standard ISO 8601 week? To quote from YearWeek doc:
ISO-8601 defines the week as always starting with Monday. The first week is the week which contains the first Thursday of the calendar year. As such, the week-based-year used in this class does not align with the calendar year.
java.time
The modern approach uses the java.time classes.
The troublesome old date-time classes such as java.util.Date, java.util.Calendar, and java.text.SimpleTextFormat are now legacy, supplanted by the java.time classes.
The Joda-Time project is now in maintenance mode, with the team advising migration to the java.time classes.
ThreeTen-Extra
The ThreeTen-Extra project extends java.time with additional functionality. This includes a handy YearWeek class, just what we need for this Question.
Specify your week-based year number and your week number.
YearWeek yw = YearWeek.of( 2017 , 1 ) ;
The LocalDate class represents a date-only value without time-of-day and without time zone.
You can ask the YearWeek object to determine the date of a day contained within its week. Specify a DayOfWeek enum object. Note that a DayOfWeek is an object rather than a mere integer or string, providing for type-safety and valid values.
LocalDate ld = yw.atDay( DayOfWeek.TUESDAY ) ;
About java.time
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?
Java SE 8, Java SE 9, and later
Built-in.
Part of the standard Java API with a bundled implementation.
Java 9 adds some minor features and fixes.
Java SE 6 and Java SE 7
Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
Android
The ThreeTenABP project adapts ThreeTen-Backport (mentioned above) for Android specifically.
See How to use ThreeTenABP….
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.

java.time
The java.util Date-Time API and their formatting API, SimpleDateFormat are outdated and error-prone. It is recommended to stop using them completely and switch to the modern Date-Time API*.
Also, quoted below is a notice from the home page of Joda-Time:
Note that from Java SE 8 onwards, users are asked to migrate to java.time (JSR-310) - a core part of the JDK which replaces this project.
Solution using java.time, the modern Date-Time API:
import java.time.DayOfWeek;
import java.time.LocalDate;
import java.time.temporal.WeekFields;
import java.util.Locale;
public class Main {
public static void main(String[] args) {
// Test
int weekNumber = 34;
int year = 2021;
System.out.println(getLocalDate(weekNumber, DayOfWeek.TUESDAY, year, Locale.UK));
System.out.println(getLocalDate(weekNumber, DayOfWeek.TUESDAY, year, Locale.US));
System.out.println(getLocalDate(weekNumber, DayOfWeek.SUNDAY, year, Locale.UK));
System.out.println(getLocalDate(weekNumber, DayOfWeek.SUNDAY, year, Locale.US));
}
static LocalDate getLocalDate(int weekNumber, DayOfWeek dow, int year, Locale locale) {
return LocalDate.of(year, 2, 1)
.with(dow)
.with(WeekFields.of(locale).weekOfWeekBasedYear(), weekNumber);
}
}
Output:
2021-08-24
2021-08-17
2021-08-29
2021-08-15
ONLINE DEMO
Note that the first day of the week is Locale-dependent e.g. it is Monday in the UK while Sunday in the US. As per the ISO 8601 standards, it is Monday. For comparison, check the US calendar and the UK calendar. Accordingly, the date will vary as shown in the example above.
Learn more about the modern Date-Time API from Trail: Date Time.
* For any reason, if you have to stick to Java 6 or Java 7, you can use ThreeTen-Backport which backports most of the java.time functionality to Java 6 & 7. If you are working for an Android project and your Android API level is still not compliant with Java-8, check Java 8+ APIs available through desugaring and How to use ThreeTenABP in Android Project.

java.util.Date to java.sql.Date conversion gives wrong month

Consider the following snippet:
Calendar futureDate = Calendar.getInstance();
int year = 2011;
int month = 11;
int day = 14;
futureDate.set(year,month, day);
System.out.println(futureDate.toString());
java.sql.Date sqlDate = new java.sql.Date( futureDate.getTime().getTime());
The printout from futureDate.toString() is:
.....YEAR=2011,MONTH=11,WEEK_OF_YEAR=43,WEEK_OF_MONTH=4,DAY_OF_MONTH=14,DAY_OF_YEAR=289,DAY_OF_WEEK=1,DAY_OF_WEEK_IN_MONTH=3,AM_PM=0,HOUR=11,HOUR_OF_DAY=11,MINUTE=32,SECOND=51,MILLISECOND=117,ZONE_OFFSET=-18000000,DST_OFFSET=3600000]
which shows that the Calendare object holds the correct date. However, after converting to sql date and storing in the database (MySQL through JDBC), the MySQL table shows '2011-12-14' for this date instead of '2011-11-14'.
I would have suspected locale and time zone, but these would cause discrepancy in the time of day not in the month part of the date.
Any clues to what I did wrong?

Calendar#set(int, int, int) interprets the month argument as zero-based, so futureDate.set(2011, 11, 14) sets the calendar's month to December.

tl;dr
LocalDate.of( 2011 , 11 , 14 ) // November 14th, 2011
Details
The Answer by Matt Ball is correct. But now there is a much improved way.
java.time
The troublesome old date-time classes such as Calendar, java.util.Date, and java.sql.Date are now legacy, supplanted by the java.time classes.
Unlike the legacy classes, the java.time classes have sane numbering, such as months being numbered 1-12 for January to December, and 1-7 for Monday to Sunday.
The LocalDate class represents a date-only value without time-of-day and without time zone.
LocalDate ld = LocalDate.of( 2011 , 11 , 14 ) ;
Or use the handy Month enum.
LocalDate ld = LocalDate.of( 2011 , Month.NOVEMBER , 14 ) ;
With a JDBC driver supporting JDBC 4.2 and later, you may pass your java.time objects directly to the database.
myPreparedStatement.setObject( … , ld ) ;
When fetching, use getObject.
LocalDate ld = myResultSet.getObject( … , LocalDate.class ) ;
About java.time
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?
Java SE 8, Java SE 9, and later
Built-in.
Part of the standard Java API with a bundled implementation.
Java 9 adds some minor features and fixes.
Java SE 6 and Java SE 7
Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
Android
The ThreeTenABP project adapts ThreeTen-Backport (mentioned above) for Android specifically.
See How to use ThreeTenABP….
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.

If I have a specific date of a day, how do I get the date of that day in the previous week?

SEE ANSWER FROM #Basil Bourque for most up to date answer
For example, if I have a "Date" variable "date1" with a value of (dd/mm/yyy) 03/07/2011, which is a Sunday. How do I get the "Date" of the previous Sunday "date2"? which would have the value (dd/mm/yyyy) 26/06/2011.
Is there an easy way of doing it, for example:
pseudo code:
Date date1 = (03/07/2011);
Date date2 = date1.subtractNumberOfDays(7);

You should use Calendar:
Calendar date = new GregorianCalendar(2011, Calendar.JULY, 3);
date.add(Calendar.DAY_OF_MONTH, -7);
System.out.println(date.getTime());
You can create a calendar from date too:
Date date1 = new Date(111, Calendar.JULY, 3);//the year field adds 1900 on to it.
Calendar date = new GregorianCalendar();
date.setTime(date1);
date.add(Calendar.DAY_OF_MONTH, -7);
date2 = date.getTime();
Be aware that:
Java uses 0 to represent January !
Date(year, month, day) is deprecated since JDK version 1.1 !
See the GregorianCalendar JavaDoc:
Constructs a GregorianCalendar with the given date set in the default time zone with the default locale.
Parameters:
year the value used to set the YEAR calendar field in the calendar.
month the value used to set the MONTH calendar field in the calendar. Month value is 0-based. e.g., 0 for January.
dayOfMonth the value used to set the DAY_OF_MONTH calendar field in the calendar.

tl;dr
LocalDate.of( 2011 , Month.JULY , 3 )
.minusWeeks( 1 )
2011-06-26
java.time
The Question and Answers use old outmoded date-time classes. Instead use the java.time classes.
LocalDate
The LocalDate class represents a date-only value without time-of-day and without time zone.
LocalDate localDate = LocalDate.of( 2011 , Month.JULY , 3 );
Alternatively, pass an integer in second argument instead of the Month enum. Pass 1-12 for January-December.
Previous week
You can subtract a week from the date.
LocalDate weekPrior = localDate.minusWeeks( 1 );
See this code run live at IdeOne.com.
Previous day-of-week
If you want a specific day of the week, use a TemporalAdjuster.
Several such handy implementations provided in the TemporalAdjusters class (note the plural 's').
LocalDate priorTuesday = localDate.with( TemporalAdjusters.previous( DayOfWeek.TUESDAY ) ) ;
About java.time
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?
Java SE 8, Java SE 9, and later
Built-in.
Part of the standard Java API with a bundled implementation.
Java 9 adds some minor features and fixes.
Java SE 6 and Java SE 7
Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
Android
The ThreeTenABP project adapts ThreeTen-Backport (mentioned above) for Android specifically.
See How to use ThreeTenABP….
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.

A more clear approach:
Calendar date = new GregorianCalendar(2011, 1, 1);
date.add(Calendar.WEEK_OF_MONTH, -1);
System.out.println(date.getTime());
use either WEEK_OF_MONTH or WEEK_OF_YEAR

If you are willing to use Joda time it will be very easy.
An example:
DateTime toDay=new DateTime();
DateTime dateOfPreviousWeek=toDay.minusDays(7);
Another:
DateTime toDay = new DateTime(2011, 7, 1, 0, 0, 0, 0);
DateTime dateOfPreviousWeek = toDay.minusDays(7);
You can get java.util.Date from DateTime as:
Date javaDate=jodaDateTime.toDate();

How to set an expiration date in java

I am trying to write some code to correctly set an expiration date given a certain date.
For instance this is what i have.
Date lastSignupDate = m.getLastSignupDate();
long expirationDate = 0;
long milliseconds_in_half_year = 15778463000L;
expirationDate = lastSignupDate.getTime() + milliseconds_in_half_year;
Date newDate = new Date(expirationDate);
However, say if i the sign up date is on 5/7/2011 the expiration date output i get is on 11/6/2011 which is not exactly half of a year from the given date. Is there an easier way to do this?

I would use the Calendar class - the add method will do this kind of thing perfectly.
http://download.oracle.com/javase/6/docs/api/java/util/Calendar.html
Date date = new Date();
Calendar cal = Calendar.getInstance();
cal.setTime(date);
cal.add(Calendar.MONTH, 6);
java.util.Date expirationDate = cal.getTime();
System.err.println(expirationDate);

Here's a simple suggestion using joda-time:
DateTime dt = new DateTime(lastSignupDate);
dt = dt.plusDays(DateTimeConstants.MILLIS_PER_DAY * 365 / 2);
// you can also use dt.plusDays(364 / 2);
You can also use a Calendar:
Calendar c = Calendar.getInstance();
c.setTime(lastSignupDate);
c.add(Calendar.MILLISECOND, MILLIS_PER_DAY * 365 / 2);
// or c.add(Calendar.DAY_OF_YEAR, 364 / 2);

tl;dr
java.time.LocalDate.of( 2011 , Month.MAY , 7 )
.plusMonths( 6 )
.toString()
2011-11-07
java.time
You are using date-time values, so you must account for issues such as time zones, anomalies, and leap year. But you only want a date without a time-of-day and without a time zone, so much easier if you use a date-only class rather than a date-with-time class.
The modern approach uses java.time rather than the troublesome legacy date-time classes.
if i the sign up date is on 5/7/2011 the expiration date output i get is on 11/6/2011 which is not exactly half of a year from the given date
The LocalDate class represents a date-only value without time-of-day and without time zone.
LocalDate ld = LocalDate.of( 2011 , Month.MAY , 7 ) ;
You can do math with the java.time classes. Look for plus… and minus… methods.
LocalDate sixMonthsLater = ld.plusMonths( 6 ) ;
Or pass the amount of time.
Period p = Period.ofMonths( 6 ) ;
LocalDate sixMonthsLater = ld.plus( p ) ;
See this code run live at IdeOne.com.
2011-05-07
2011-11-07
About java.time
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?
Java SE 8, Java SE 9, and later
Built-in.
Part of the standard Java API with a bundled implementation.
Java 9 adds some minor features and fixes.
Java SE 6 and Java SE 7
Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
Android
Later versions of Android bundle implementations of the java.time classes.
For earlier Android, the ThreeTenABP project adapts ThreeTen-Backport (mentioned above). See How to use ThreeTenABP….
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.

Do you really need an expiration-date, which is accurate to the millisecond?
I would implement it as 6 Months from x.
Jan. 1 => Jul 1
Sep. 28=> Feb 28
Sep. 29=> Feb 28
Sep. 30=> Feb 28
Oct. 1=> Mar 1
Maybe you like to be generous, and say 'Mar 1' for 'Sep 29 and 30' too.

Here's an example of using Date with TimeUnit that's a little more readable:
long year = TimeUnit.MILLISECONDS.convert(365, TimeUnit.DAYS);
Date expiry = new Date(System.currentTimeMillis() + year);
System.out.println(expiry);
Shame it doesn't have year and day, look at GregorianCalendar or Jodatime for a better API.

Calendar calendar = Calendar.getInstance();
calendar.setTimeInMillis(new Date().getTime());
// 10 minutes expiration time
calendar.add(calendar.MINUTE, 10);
// prints 10 minutes ahead time
System.out.println(new Date(calendar.getTime().getTime()));

Ask Gregorian Calendar for hour of day in java

I'm using a Gregorian Calendar to set a specific date and time to an application using the set function of the Gregorian Calendar. When i use the getTime() method, it gives me the right output however when i try to access the Hour_Of_Day and Minute it gives a wrong number.
Calendar time = new GregorianCalendar();
time.set(2010, Calendar.JANUARY, 1, 7, 20,0);
hour = time.HOUR_OF_DAY;
minute = time.MINUTE;
The hour gives an output of 11 and the minute gives an a value of 12.
Any suggestions on how to fix this?
Thanks

Your code is just assigning hour/minute to constants. You need to call Calendar.get(int):
hour = time.get(Calendar.HOUR_OF_DAY);
minute = time.get(Calendar.MINUTE);

tl;dr
myGregCal
.toZonedDateTime() // Convert from legacy class GregorianCalendar to modern ZonedDateTime.
.getHour() // Get hour-of-day, 0-23.
java.time
Much easier with the modern java.time classes that replace those troublesome old legacy date-time classes.
The ZonedDateTime class represents a moment on the timeline in a specific time zone with a resolution of nanoseconds.
Convert from your GregorianCalendar using new methods added to the old classes.
ZonedDateTime zdt = myGregCal.toZonedDateTime() ;
Or start fresh without the GregorianCalendar class.
ZoneId z = ZoneId.of( "America/Montreal" );
ZonedDateTime zdt = ZonedDateTime.of( 2010 , Month.JANUARY , 1 , 7 , 20 , 0 , 0 , z );
If you want to work with just the time-of-day portion, extract a LocalTime.
LocalTime localTime = zdt.toLocalTime() ;
If you really want the integer numbers of hours and minutes, you can interrogate for those.
int hour = zdt.getHour();
int minute = zdt.getMinute();
About java.time
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?
Java SE 8 and SE 9 and later
Built-in.
Part of the standard Java API with a bundled implementation.
Java 9 adds some minor features and fixes.
Java SE 6 and SE 7
Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
Android
The ThreeTenABP project adapts ThreeTen-Backport (mentioned above) for Android specifically.
See How to use ThreeTenABP….
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.