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Set time to 00:00:00

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How to make time as zero in date in Java?

set(Calendar. HOUR_OF_DAY, 0); calendar. set(Calendar. MINUTE, 0); calendar.

How change Calendar time in Java?

Calendar setTime() Method in Java with ExamplesThe setTime(Date dt) method in Calendar class is used to set Calendars time represented by this Calendar's time value, with the given or passed date as a parameter. Parameters: The method takes one parameter dt of Date type and refers to the given date that is to be set.

How do I set LocalDateTime to start of day?

Another way in which we can achieve the same result is by using the of() method, providing a LocalDate and one of the LocalTime's static fields: LocalDateTime startOfDay = LocalDateTime. of(localDate, LocalTime. MIDNIGHT);

How do I find my LocalDate date?

1. LocalDate. LocalDate is an immutable class that represents Date with default format of yyyy-MM-dd. We can use now() method to get the current date.


Use another constant instead of Calendar.HOUR, use Calendar.HOUR_OF_DAY.

calendar.set(Calendar.HOUR_OF_DAY, 0);

Calendar.HOUR uses 0-11 (for use with AM/PM), and Calendar.HOUR_OF_DAY uses 0-23.

To quote the Javadocs:

public static final int HOUR

Field number for get and set indicating the hour of the morning or afternoon. HOUR is used for the 12-hour clock (0 - 11). Noon and midnight are represented by 0, not by 12. E.g., at 10:04:15.250 PM the HOUR is 10.

and

public static final int HOUR_OF_DAY

Field number for get and set indicating the hour of the day. HOUR_OF_DAY is used for the 24-hour clock. E.g., at 10:04:15.250 PM the HOUR_OF_DAY is 22.

Testing ("now" is currently c. 14:55 on July 23, 2013 Pacific Daylight Time):

public class Main
{
   static SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

    public static void main(String[] args)
    {
        Calendar now = Calendar.getInstance();
        now.set(Calendar.HOUR, 0);
        now.set(Calendar.MINUTE, 0);
        now.set(Calendar.SECOND, 0);
        System.out.println(sdf.format(now.getTime()));
        now.set(Calendar.HOUR_OF_DAY, 0);
        System.out.println(sdf.format(now.getTime()));
    }
}

Output:

$ javac Main.java
$ java Main
2013-07-23 12:00:00
2013-07-23 00:00:00

java.time

Using the java.time framework built into Java 8 and later. See Tutorial.

import java.time.LocalTime;
import java.time.LocalDateTime;

LocalDateTime now = LocalDateTime.now(); # 2015-11-19T19:42:19.224
# start of a day
now.with(LocalTime.MIN); # 2015-11-19T00:00
now.with(LocalTime.MIDNIGHT); # 2015-11-19T00:00

If you do not need time-of-day (hour, minute, second etc. parts) consider using LocalDate class.

LocalDate.now(); # 2015-11-19

Here are couple of utility functions I use to do just this.

/**
 * sets all the time related fields to ZERO!
 *
 * @param date
 *
 * @return Date with hours, minutes, seconds and ms set to ZERO!
 */
public static Date zeroTime( final Date date )
{
    return DateTimeUtil.setTime( date, 0, 0, 0, 0 );
}

/**
 * Set the time of the given Date
 *
 * @param date
 * @param hourOfDay
 * @param minute
 * @param second
 * @param ms
 *
 * @return new instance of java.util.Date with the time set
 */
public static Date setTime( final Date date, final int hourOfDay, final int minute, final int second, final int ms )
{
    final GregorianCalendar gc = new GregorianCalendar();
    gc.setTime( date );
    gc.set( Calendar.HOUR_OF_DAY, hourOfDay );
    gc.set( Calendar.MINUTE, minute );
    gc.set( Calendar.SECOND, second );
    gc.set( Calendar.MILLISECOND, ms );
    return gc.getTime();
}

One more JAVA 8 way:

LocalDateTime localDateTime = LocalDateTime.now().truncatedTo(ChronoUnit.HOURS);

But it's a lot more useful to edit the date that already exists.


You would better to primarily set time zone to the DateFormat component like this:

DateFormat dateFormat = new SimpleDateFormat("HH:mm:ss");
dateFormat.setTimeZone(TimeZone.getTimeZone("GMT"));

Then you can get "00:00:00" time by passing 0 milliseconds to formatter:

String time = dateFormat.format(0);

or you can create Date object:

Date date = new Date(0); // also pass milliseconds
String time = dateFormat.foramt(date);

or you be able to have more possibilities using Calendar component but you should also set timezone as GMT to calendar instance:

Calendar calendar = Calendar.getInstance(TimeZone.getTimeZone("GMT"), Locale.US);
calendar.set(Calendar.HOUR_OF_DAY, 5);
calendar.set(Calendar.MINUTE, 37);
calendar.set(Calendar.SECOND, 27);

dateFormat.format(calendar.getTime());

tl;dr

myJavaUtilDate                                 // The terrible `java.util.Date` class is now legacy. Use *java.time* instead.
.toInstant()                                   // Convert this moment in UTC from the legacy class `Date` to the modern class `Instant`.
.atZone( ZoneId.of( "Africa/Tunis" ) )         // Adjust from UTC to the wall-clock time used by the people of a particular region (a time zone).
.toLocalDate()                                 // Extract the date-only portion.
.atStartOfDay( ZoneId.of( "Africa/Tunis" ) )   // Determine the first moment of that date in that zone. The day does *not* always start at 00:00:00.

java.time

You are using terrible old date-time classes that were supplanted years ago by the modern java.time classes defined in JSR 310.

DateInstant

A java.util.Date represent a moment in UTC. Its replacement is Instant. Call the new conversion methods added to the old classes.

Instant instant = myJavaUtilDate.toInstant() ;

Time zone

Specify the time zone in which you want your new time-of-day to make sense.

Specify a proper time zone name in the format of Continent/Region, such as America/Montreal, Africa/Casablanca, or Pacific/Auckland. Never use the 2-4 letter abbreviation such as EST or IST as they are not true time zones, not standardized, and not even unique(!).

ZoneId z = ZoneId.of( "America/Montreal" ) ;

ZonedDateTime

Apply the ZoneId to the Instant to get a ZonedDateTime. Same moment, same point on the timeline, but different wall-clock time.

ZonedDateTime zdt = instant.atZone( z ) ;

Changing time-of-day

You asked to change the time-of-day. Apply a LocalTime to change all the time-of-day parts: hour, minute, second, fractional second. A new ZonedDateTime is instantiated, with values based on the original. The java.time classes use this immutable objects pattern to provide thread-safety.

LocalTime lt = LocalTime.of( 15 , 30 ) ;  // 3:30 PM.
ZonedDateTime zdtAtThreeThirty = zdt.with( lt ) ; 

First moment of day

But you asked specifically for 00:00. So apparently you want the first moment of the day. Beware: some days in some zones do not start at 00:00:00. They may start at another time such as 01:00:00 because of anomalies such as Daylight Saving Time (DST).

Let java.time determine the first moment. Extract the date-only portion. Then pass the time zone to get first moment.

LocalDate ld = zdt.toLocalDate() ;
ZonedDateTime zdtFirstMomentOfDay = ld.atStartOfDay( z ) ;

Adjust to UTC

If you need to go back to UTC, extract an Instant.

Instant instant = zdtFirstMomentOfDay.toInstant() ;

InstantDate

If you need a java.util.Date to interoperate with old code not yet updated to java.time, convert.

java.util.Date d = java.util.Date.from( instant ) ;