Question

import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;

public class test {

    /*
     * Calculate the difference between two date/times   * 
     * 
     */

    private static long dateDiff(Date toDate, Date fromDate) {
        Calendar cal = Calendar.getInstance();
        cal.setTime(toDate);
        long ms = cal.getTimeInMillis();
        cal.setTime(fromDate);
        ms -= cal.getTimeInMillis();
        return ms;
    }

    public static void main(String[] args) {

        SimpleDateFormat sdf = new SimpleDateFormat("hh:mm:ss");
        Date d1 = null;
        Date d2 = null;

        try {
            d1 = sdf.parse("11:00:00");
            d2 = sdf.parse("10:00:00");
        } catch (Exception e) {
            e.printStackTrace();
        }

        long result = dateDiff(d1, d2);

        Date time = new Date(result);

        System.out.println(time);
    }
}

When I run it I get this result :

Thu Jan 01 02:00:00 CET 1970

I would expect 1 hour difference ?! again a problem with Timezone??

Any idea how I can fix it.

thx all

Answer 1

I don’t know what you expect this to do, but what you are actually doing is outputting the date corresponding to one hour after midnight on Jan 1 1970, using the default timezone.

You seem to want to Date to represent a duration (i.e. a number of seconds). It doesn’t do that, and neither will the Date formatters render a Date as a duration.

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I need the time difference between two Date fields and then put it in MySql (time format)

For what you are trying to do, you need calculate the duration value as a long, then use the java.sql.Time(long) constructor to create a Time object. You can either serialize this object using its toString() method or use it as a parameter in a JDBC prepared statement.

It turns out that my advice above is incorrect too.

Your real problem is that the SQL Time type is for representing times … not durations. In fact, SQL does not have a dedicated duration type, so the best you can do is represent the duration as an integer number of seconds or milliseconds or whatever.

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(For the more general case, the Joda Time libraries are generally thought to provide the best APIs for manipulating dates, times and related temporal values. But for this simple case, the standard J2SE libraries should suffice … provided that you use them correctly.)