In java how do we round off time to nearest hour and minute?

Question

I have a String which has the time. I need to round it off to the nearest hour and also the nearest minute. How do I do it in java? Ex: String time="12:58:15"; I need to round it off to 1:00:00 and also 12:58:00

Possible solution here http://stackoverflow.com/questions/3553964/how-to-round-time-to-the-nearest-quarter-in-java — r0ast3d, Nov 22 '11 at 20:19

score 22 · Answer 1 · edited Oct 20 '15 at 20:59

For calendar operations you have to use Calendar class. In your case you would do something like this:

package test;

import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;

public class TestDate {

    public static void main(String[] args) {
        Calendar c = new GregorianCalendar();
        c.set(Calendar.HOUR_OF_DAY, 12);
        c.set(Calendar.MINUTE, 58);
        c.set(Calendar.SECOND, 15);
        Date d = c.getTime();

        System.out.println("Start point: " + d.toString());
        System.out.println("Nearest whole minute: " + toNearestWholeMinute(d));
        System.out.println("Nearest whole hour: " + toNearestWholeHour(d));
    }

    static Date toNearestWholeMinute(Date d) {
        Calendar c = new GregorianCalendar();
        c.setTime(d);

        if (c.get(Calendar.SECOND) >= 30)
            c.add(Calendar.MINUTE, 1);

        c.set(Calendar.SECOND, 0);

        return c.getTime();
    }

    static Date toNearestWholeHour(Date d) {
        Calendar c = new GregorianCalendar();
        c.setTime(d);

        if (c.get(Calendar.MINUTE) >= 30)
            c.add(Calendar.HOUR, 1);

        c.set(Calendar.MINUTE, 0);
        c.set(Calendar.SECOND, 0);

        return c.getTime();
    }

}

And the result:

Start point: Tue Nov 22 12:58:15 CET 2011
Nearest whole minute: Tue Nov 22 12:58:00 CET 2011
Nearest whole hour: Tue Nov 22 13:00:00 CET 2011

Thanks for the reply. I need to be using a String object as mentioned above as I would be getting it from a text file. — Srinivas, Nov 23 '11 at 15:46
when rounding, you should also set `Calendar.MILLISECOND` to `0`, not just seconds (and minutes). — oezi, Jul 31 '13 at 12:41
Um, you "have" to use the `Calendar` class? No. You can do this logic raw using the primative `long`. For example: `long now = System.currentTimeMillis(); long rounded = now - now % 60000;` Once you have a long you can do whatever you want. — Blake, Jan 12 '18 at 16:23

Baked Inhalf · Answer 2 · 2019-05-28T05:33:47.083

8

With Java 8 you can use a java.time.LocalDateTime or ZonedDateTime (timezone). This would get you started by rounding to the nearest hour:

String mytime = "2019-05-21 13:41:50";

// Convert String to LocalDateTime
DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
LocalDateTime localDateTime = LocalDateTime.parse(mytime, dtf);

// If minutes equals 30 or more, add 1 hour
int minutes = localDateTime.getMinute();
if (minutes >= 30)
{
    localDateTime = localDateTime.plusHours(1);
}

// Round down
localDateTime = localDateTime.truncatedTo(ChronoUnit.HOURS)

// Back to String (OP wants the end result to be of type String)    
String roundedTime = dtf.format(localDateTime);
System.out.println(roundedTime);

For example: "2019-05-21 13:41:50" would be printed as 2019-05-21 14:00:00

edited May 28 '19 at 05:33

answered May 21 '19 at 06:41

Baked Inhalf

3,375
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4

For rounding down to whole hour I recommend `localDateTime.truncatedTo(ChronoUnit.HOURS)` (it will get rid of any nanoseconds too). – Ole V.V. May 23 '19 at 16:41
@OleV.V. Yes you are correct. In my answer above the DateTImeFormatter would "take care" of it as well, since the end result is a String. I will update my answer! – Baked Inhalf May 28 '19 at 05:32

score 1 · Answer 3 · answered Nov 22 '11 at 20:30

1

One way is to first convert it into a Date using SimpleDateFormat and its parse method (The javadoc will explain the format you need). Then you can look at the seconds and determine whether you should go up a minute or down (if it goes up, set the seconds to 0 and add a minute). Likewise for the hour, just look at minutes and if it's less than 30, round down and if greater than thirty set to zero and increase the hour.

answered Nov 22 '11 at 20:30

AHungerArtist

9,332
17
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Thanks for the reply. I need to be using a String object as mentioned above as I would be getting it from a text file. – Srinivas Nov 23 '11 at 15:46
You can use the simple date format to convert to date, perform your work, then use it to convert back to String. Probably a lot more reliable than parsing all the possible permutations of the string. But, you can do it the hard way if you wish. – AHungerArtist Nov 23 '11 at 17:58

score 0 · Answer 4 · answered Jun 10 '15 at 21:57

package com.xyz.util;

import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;

public class DateTimeUtils {

    public static void main(String[] args) {
        Date date = new Date();
        date.setHours(23);
        System.out.println("prev whole hour, millies: "+toWholeHour(date,-1)+", "+toWholeHour(date,-1).getTime());
        System.out.println("curr whole hour, millies: "+toWholeHour(date,0)+", "+toWholeHour(date,0).getTime());
        System.out.println("next whole hour, millies: "+toWholeHour(date,1)+", "+toWholeHour(date,1).getTime());

        System.out.println("prev whole minute, millies: "+toWholeMinute(date,-1)+", "+toWholeMinute(date,-1).getTime());
        System.out.println("curr whole minute, millies: "+toWholeMinute(date,0)+", "+toWholeMinute(date,0).getTime());
        System.out.println("next whole minute, millies: "+toWholeMinute(date,1)+", "+toWholeMinute(date,1).getTime());
    }

    public static Date toWholeHour(Date d, int beforeOrAfter) {
        Calendar c = new GregorianCalendar();
        c.setTime(d);
        c.add(Calendar.HOUR, beforeOrAfter);
        c.set(Calendar.MINUTE, 0);
        c.set(Calendar.SECOND, 0);
        c.set(Calendar.MILLISECOND, 0);
        return c.getTime();
    }

    public static Date toWholeMinute(Date d, int beforeOrAfter) {
        Calendar c = new GregorianCalendar();
        c.setTime(d);
        c.add(Calendar.MINUTE, beforeOrAfter);
        c.set(Calendar.SECOND, 0);
        c.set(Calendar.MILLISECOND, 0);
        return c.getTime();
    }

}

FrancescoM · Answer 5 · 2020-07-07T09:31:27.227

0

Well, the best answer is the simplest one

  /**
   * 2020-01-01 10:00:55 is transformed into 2020-01-01 10:00:00
   * 2020-01-01 10:20:55 is transformed into 2020-01-01 10:00:00
   * 2020-01-01 10:30:01 is transformed into 2020-01-01 11:00:00
   * @return the Timestamp rounded to the nearest hour
   */
  public static Timestamp roundTimestampToNearestHour(Timestamp input){
    return Timestamp.from(Instant.ofEpochMilli(((input.getTime()+1800000)/(60000*60))*(60000*60)));
}

edited Jul 07 '20 at 09:31

answered Feb 06 '20 at 17:20

FrancescoM

1,400
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what is the 1800000 doing? – Oxnard Feb 28 '23 at 20:56

score 0 · Answer 6 · answered Nov 22 '11 at 20:49

0

Create a Date using SimpleDateFormat. Create GregorianCalendar from the Date. Roll the minutes or seconds by 30. Then set minutes or seconds to 0.

answered Nov 22 '11 at 20:49

James A. N. Stauffer

2,649
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Thanks for the reply. I need to be using a String object as mentioned above as I would be getting it from a text file. – Srinivas Nov 23 '11 at 15:45

In java how do we round off time to nearest hour and minute?

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