Asked  7 Months ago    Answers:  5   Viewed   27 times

For Example I have the date: "23/2/2010" (23th Feb 2010). I want to pass it to a function which would return the day of week. How can I do this?

In this example, the function should return String "Tue".

Additionally, if just the day ordinal is desired, how can that be retrieved?

 Answers

29

Yes. Depending on your exact case:

  • You can use java.util.Calendar:

    Calendar c = Calendar.getInstance();
    c.setTime(yourDate);
    int dayOfWeek = c.get(Calendar.DAY_OF_WEEK);
    
  • if you need the output to be Tue rather than 3 (Days of week are indexed starting at 1 for Sunday, see Calendar.SUNDAY), instead of going through a calendar, just reformat the string: new SimpleDateFormat("EE").format(date) (EE meaning "day of week, short version")

  • if you have your input as string, rather than Date, you should use SimpleDateFormat to parse it: new SimpleDateFormat("dd/M/yyyy").parse(dateString)

  • you can use joda-time's DateTime and call dateTime.dayOfWeek() and/or DateTimeFormat.

  • edit: since Java 8 you can now use java.time package instead of joda-time

Tuesday, June 1, 2021
 
scessor
answered 7 Months ago
46

I've tested this with JDK 1.8.0_131 for Mac OS X and JDK 1.8.0111 for Windows (both worked).

I've created a DateTimeFormatter with optional sections (delimited by []), to parse both cases (MM/dd/yyyy and yyyy-MM-dd'T'HH:mm:ss).

The same formatter worked for your case (LocalDate), but there are some considerations below.

// parse both formats (use optional section, delimited by [])
DateTimeFormatter parser = DateTimeFormatter.ofPattern("[MM/dd/yyyy][yyyy-MM-dd'T'HH:mm:ss]");

// parse MM/dd/yyyy
LocalDate d1 = LocalDate.parse("10/16/2016", parser);
// parse yyyy-MM-dd'T'HH:mm:ss
LocalDate d2 = LocalDate.parse("2016-10-16T10:20:30", parser);

// parser.format(d1) is the same as d1.format(parser)
System.out.println(parser.format(d1));
System.out.println(parser.format(d2));

The output is:

10/16/2016
10/16/2016


PS: this works only with LocalDate. If I try to format an object with time fields (like LocalDateTime), both formats are used:

System.out.println(parser.format(LocalDateTime.now()));

This prints:

06/18/20172017-06-18T07:40:55

Note that it formatted with both patterns. My guess is that the formatter checks if the object has the fields in each optional section. As the LocalDate has no time fields (hour/minute/second), the second pattern fails and it prints only the first one (MM/dd/yyyy). But the LocalDateTime has all the time fields, and both patterns are valid, so both are used to format.

My conclusion is: this isn't a general solution (like the Joda-Time's version), it's more like a "lucky" case where the patterns involved created the desired situation. But I wouldn't rely on that for all cases.

Anyway, if you are only using LocalDate, you can try to use this code. But if you're working with another types, then you'll probably have to use another formatter for the output, like this:

// parser/formatter for month/day/year
DateTimeFormatter mdy = DateTimeFormatter.ofPattern("MM/dd/yyyy");
// parser for both patterns
DateTimeFormatter parser = new DateTimeFormatterBuilder()
    // optional MM/dd/yyyy
    .appendOptional(mdy)
    // optional yyyy-MM-dd'T'HH:mm:ss (use built-in formatter)
    .appendOptional(DateTimeFormatter.ISO_LOCAL_DATE_TIME)
    // create formatter
    .toFormatter();

// parse MM/dd/yyyy
LocalDate d1 = LocalDate.parse("10/16/2016", parser);
// parse yyyy-MM-dd'T'HH:mm:ss
LocalDate d2 = LocalDate.parse("2016-10-16T10:20:30", parser);

// use mdy to format
System.out.println(mdy.format(d1));
System.out.println(mdy.format(d2));

// format object with time fields: using mdy formatter to avoid multiple pattern problem
System.out.println(mdy.format(LocalDateTime.now()));

The output is:

10/16/2016
10/16/2016
06/18/2017

Friday, July 2, 2021
 
Anax
answered 6 Months ago
44

check jsFiddle

JavaScript Code

var newdate = new Date();
newdate.setDate(newdate.getDate()+252);   // 36 week * 7 day = 252
alert(newdate.getFullYear() + "-" + (newdate.getMonth() + 1) + "-" + newdate.getDate());  // alert(newdate);
Wednesday, September 1, 2021
 
Kasun Sandaruwan
answered 3 Months ago
17

As suggested by other users, you need to also set the millisecond value of the calendars to zero to compare only the dates. This can be achieved with the following code snippet:

someCalendar.set(Calendar.MILLISECOND, 0)

Also, note that timezone changes (e.g. moving from winter time to summer time) may mean there is more or less than 86,400,000 ms in a day.

Sunday, October 31, 2021
 
deadcell4
answered 1 Month ago
81
dat <- as.Date( c("2010-04-02", "2010-04-06", "2010-04-09", "2010-04-10", "2010-04-14", 
       "2010-04-15", "2010-04-19",   "2010-04-21", "2010-04-22", "2010-04-23","2010-04-24", 
        "2010-04-25", "2010-04-26", "2010-04-28", "2010-04-29", "2010-04-30"))
 dwka <- format(dat , "%a")
 dwka
# [1] "Fri" "Tue" "Fri" "Sat" "Wed" "Thu" "Mon"
#  [8] "Wed" "Thu" "Fri" "Sat" "Sun" "Mon" "Wed"
# [15] "Thu" "Fri"
dwkn <- as.numeric( format(dat , "%w") ) # numeric version
hist( dwkn , breaks= -.5+0:7, labels= unique(dwka[order(dwkn)]))

enter image description here

Wednesday, November 10, 2021
 
St.Antario
answered 3 Weeks ago
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