Question

I’m trying to convert a running pace that I get in the format of a String (say : “5:00” for a 5 min/mile). (I am converting min/mile to min/km).

So here’s what I’m doing :

String milePace = "05:00";
DateFormat sdf = new SimpleDateFormat("mm:ss");
Date date = sdf.parse(milePace);

Calendar cal = Calendar.getInstance();
cal.setTime(date);

long mileTime = cal.getTimeInMillis();
long kmPace = Math.round(mileTime * 0.623712);

cal.setTimeInMillis(kmPace);

This unfortunately makes sense to me, but does not work.

0.623712 would be the converting unit and does work (as long as I am concerned).

When I check the value of mileTime I get 18240000. As far I can see, this is the issue as this value should be 240000 (which would be 4mins * 60 secs * 1000)

Is there an issue with the code or is there something from the cal function that would give me that extra 18000000 miliseconds?

Thanks in advance!

Answer 1

getTimeInMillis() returns the number of milliseconds since 1970 UTC. It will be affected by the time zone of your parser, and what date the parser decides to use for your input.

I would suggest that you use Joda Time and parse the value as a Period instead.

Sample code:

import org.joda.time.*;
import org.joda.time.format.*;
import java.util.*;

public class Test {
    public static void main(String[] args) {
        String text = "05:00";

        PeriodFormatter formatter = new PeriodFormatterBuilder()
            .minimumPrintedDigits(2)
            .appendMinutes()
            .appendSeparator(":")
            .appendSeconds()
            .toFormatter();

        Period milePeriod = formatter.parsePeriod(text);

        long mileMillis = milePeriod.toStandardDuration().getMillis();
        long kmMillis = Math.round(mileMillis * 0.623712);

        PeriodType minutesSeconds = PeriodType.time()
            .withMillisRemoved()
            .withHoursRemoved();

        Period kmPeriod = new Period(kmMillis, minutesSeconds);

        System.out.println(formatter.print(kmPeriod)); // Prints 03:07
    }
}