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

Question

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!

Answer 1

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.

Answer 2

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

Answer 3

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));

Answer 4

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()));

Answer 5

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!

Answer 6

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 ) ; 

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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 .