What's the most efficient way to strip out the time from a Java Date object?

Question

What's the most efficient way to remove the time portion from a Java date object using only Classes from within the JDK?

I have the following

myObject.getDate() = {java.util.Date}"Wed May 26 23:59:00 BST 2010"

To reset the time back to 00:00:00, I'm doing the following

SimpleDateFormat sdf = new SimpleDateFormat("dd/MM/yyyy");
Date myDate = sdf.parse(sdf.format(myObject.getDate()));

The output is now

myDate = {java.util.Date}"Wed May 26 00:00:00 BST 2010"

Is there a better way to achieve the same result?

Consider JODA Time. http://joda-time.sourceforge.net/ ; much more pleasant to work with. Also http://stackoverflow.com/questions/2901262/why-were-most-java-util-date-methods-deprecated — polygenelubricants, Aug 25 '10 at 13:17
Not an option for me I'm afraid. I'm working with a third party app that won't allow for additional jars to be added. — Pram, Aug 25 '10 at 13:19

kgiannakakis · Accepted Answer · 2010-08-26T06:27:12.087

10

More verbose, but probably more efficient:

    Calendar cal = GregorianCalendar.getInstance();
    cal.setTime(date);
    // cal.set(Calendar.HOUR, 0);   // As jarnbjo pointed out this isn't enough
    cal.set(Calendar.HOUR_OF_DAY, 0);
    cal.set(Calendar.MINUTE, 0);
    cal.set(Calendar.SECOND, 0);
    cal.set(Calendar.MILLISECOND, 0);

Also, you don't need to worry about locale settings, which may cause problems with string to date conversions.

edited Aug 26 '10 at 06:27

answered Aug 25 '10 at 13:24

kgiannakakis

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I've just tried this out and I get the following output myDate = {java.util.Date}"Wed May 26 12:00:00 BST 2010" – Pram Aug 25 '10 at 13:55
Are you perhaps formatting the date in 12h instead of a 24h setting? – kgiannakakis Aug 25 '10 at 14:05
I'm getting a Date object out of cal by calling cal.getTime() – Pram Aug 25 '10 at 14:44
1

`GregorianCalendar.getInstance();` does nothing other than `Calendar.getInstance();`. It's a static method of the Calendar class, this is just an unnecessary import. – Sean Patrick Floyd Aug 25 '10 at 15:03
5

You must use cal.set(Calendar.HOUR_OF_DAY, 0). Calendar.HOUR is just the 12-hour-field of the calendar and will leave the AM_PM field unchanged, causing the 24-hour-field to be set to either 0 or 12. – jarnbjo Aug 25 '10 at 15:10
`GregorianCalendar.getInstance();` is not the same as `Calendar.getInstance();`. The later takes the current timezone and locale into account and may return something different than GegorianCalendar. – whiskeysierra Aug 26 '10 at 07:00
@whiskeysierra, `GregorianCalendar` doesn't declare any `getInstance` methods, so `GregorianCalendar.getInstance()` is just an odd way of invoking `Calendar.getInstance()`. In my opinion these "indirect" static invocations shouldn't have be allowed and should be avoided. – Daniel Lubarov Nov 27 '13 at 03:16

score 8 · Answer 2 · edited May 23 '17 at 12:10

If you have Apache commons, you can use DateUtils.truncate():

Date myDate = DateUtils.truncate(myObject.getDate(), Calendar.DATE)

^{(If you don't have access to Apache Commons, DateUtils.truncate() is implemented basically the same as kgiannakakis's answer.)}

Now, if you want "clever" code that is very fast, and you don't mind using deprecated functions from java.util.Date, here is another solution. (Disclaimer: I wouldn't use this code myself. But I have tested it and it works, even on days when DST starts/ends.)

long ts = myObject.getDate().getTime() - myObject.getDate().getTimezoneOffset()*60000L;
Date myDate = new Date(ts - ts % (3600000L*24L));
myDate.setTime(myDate.getTime() + myDate.getTimezoneOffset()*60000L);

score 1 · Answer 3 · edited May 23 '17 at 10:30

1

These methods are deprecated, but given a Date, you can do something like this:

Date d = ...;
d.setHours(0);
d.setMinutes(0);
d.setSeconds(0);

You should use a Calendar if possible. You'd then use the cal.set(Calendar.MINUTE, 0), etc.

It should be mentioned that if it's at all an option, you should use Joda-Time.

What's the most efficient way to strip out the time from a Java Date object?

5 Answers5

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