milliseconds to days

For simple cases like this, TimeUnit should be used. TimeUnit usage is a bit more explicit about what is being represented and is also much easier to read and write when compared to doing all of the arithmetic calculations explicitly. For example, to calculate the number days from milliseconds, the following statement would work:

    long days = TimeUnit.MILLISECONDS.toDays(milliseconds);

For cases more advanced, where more finely grained durations need to be represented in the context of working with time, an all encompassing and modern date/time API should be used. For JDK8+, java.time is now included (here are the tutorials and javadocs). For earlier versions of Java joda-time is a solid alternative.

If you don't have another time interval bigger than days:

int days = (int) (milliseconds / (1000*60*60*24));

If you have weeks too:

int days = (int) ((milliseconds / (1000*60*60*24)) % 7);
int weeks = (int) (milliseconds / (1000*60*60*24*7));

It's probably best to avoid using months and years if possible, as they don't have a well-defined fixed length. Strictly speaking neither do days: daylight saving means that days can have a length that is not 24 hours.

Go for TImeUnit in java

In order to import use, java.util.concurrent.TimeUnit

long millisec=System.currentTimeMillis();
long seconds=TimeUnit.MILLISECONDS.toSeconds(millisec);
long minutes=TimeUnit.MILLISECONDS.toMinutes(millisec);
long hours=TimeUnit.MILLISECONDS.toMinutes(millisec);
long days=TimeUnit.MILLISECONDS.toDays(millisec);

java.time

You can use java.time.Duration which is modelled on ISO-8601 standards and was introduced with Java-8 as part of JSR-310 implementation. With Java-9 some more convenient methods were introduced.

Demo:

import java.time.Duration;

public class Main {
    public static void main(String[] args) {
        // Duration between the two instants
        Duration duration = Duration.ofMillis(1234567890L);

        // Print Duration#toString
        System.out.println(duration);

        // Custom format
        // ####################################Java-8####################################
        String formattedElapsedTime = String.format(
                "%d Day %02d Hour %02d Minute %02d Second %d Millisecond (%d Nanosecond)", duration.toDays(),
                duration.toHours() % 24, duration.toMinutes() % 60, duration.toSeconds() % 60,
                duration.toMillis() % 1000, duration.toNanos() % 1000000000L);
        System.out.println(formattedElapsedTime);
        // ##############################################################################

        // ####################################Java-9####################################
        formattedElapsedTime = String.format("%d Day %02d Hour %02d Minute %02d Second %d Millisecond (%d Nanosecond)",
                duration.toDaysPart(), duration.toHoursPart(), duration.toMinutesPart(), duration.toSecondsPart(),
                duration.toMillisPart(), duration.toNanosPart());
        System.out.println(formattedElapsedTime);
        // ##############################################################################
    }
}

A sample run:

PT342H56M7.89S
14 Day 06 Hour 56 Minute 07 Second 890 Millisecond (890000000 Nanosecond)
14 Day 06 Hour 56 Minute 07 Second 890 Millisecond (890000000 Nanosecond)

Learn more about the modern date-time API from Trail: Date Time.

milliseconds to days

java.time

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