Convert time unit to duration in Java

java.util.concurrent.TimeUnit represents time durations in Java at a given unit of granularity and provides utility methods to convert across units. java.util.concurrent.TimeUnit was introduced back in the old Java days (1.5) but since then it has been extended several times already. In this blog post you will learn how to use java.util.concurrent.TimeUnit to convert a given time unit to a duration .

Prerequisites

You will need JDK 11+ for the examples to work.

Learn how to manage multiple Java SDKs with SDKMAN! with ease

Problem

Convert a given time unit to duration in Java

Solution

Use java.concurrent.TimeUnit enum.

Java 11

• TimeUnit.convert(Duration duration):

long yearInMillis = TimeUnit.MILLISECONDS.convert(Duration.ofDays(365));
long hourInMillis = TimeUnit.MILLISECONDS.convert(Duration.ofHours(1));
long minuteInMillis = TimeUnit.MILLISECONDS.convert(Duration.ofMinutes(1));

• TimeUnit.convert(Duration duration) with java.time.ChronoUnit:

long yearInMillis = TimeUnit.MILLISECONDS.convert(Duration.of(365, TimeUnit.DAYS.toChronoUnit()));
long hourInMillis = TimeUnit.MILLISECONDS.convert(Duration.of(1, TimeUnit.HOURS.toChronoUnit()));
long minuteInMillis = TimeUnit.MILLISECONDS.convert(Duration.of(1, TimeUnit.MINUTES.toChronoUnit()));

Pre-Java 11

• Generic TimeUnit.convert(long sourceDuration, TimeUnit sourceUnit)

long yearInMillis = TimeUnit.DAYS.toMillis(365);
long hourInMillis = TimeUnit.HOURS.toMillis(1);
long minuteInMillis = TimeUnit.MINUTES.toMillis(1);

• TimeUnit.toMillis(long duration), TimeUnit.toSeconds(long duration) etc. methods:

long yearInMillis = TimeUnit.MILLISECONDS.convert(365, TimeUnit.DAYS);
long hourInMillis = TimeUnit.MILLISECONDS.convert(1, TimeUnit.HOURS);
long minuteInMillis = TimeUnit.MILLISECONDS.convert(1, TimeUnit.MINUTES);

Final example

class Java11TimeUnitConvertTests {

    public static final long DAYS_IN_A_YEAR = 365L;
    public static final long HOURS_IN_A_DAY = 24L;
    public static final long MINUTES_IN_AN_HOUR = 60L;
    public static final long SECONDS_IN_A_MINUTE = 60L;
    public static final long MILLISECONDS_IN_A_SECOND = 1000L;
    @Test
    void aYearInMillis() {

        // A year in milliseconds
        long yearInMillis = TimeUnit.MILLISECONDS.convert(Duration.ofDays(365)); // since Java 11

        assertThat(yearInMillis)
                .isEqualTo(DAYS_IN_A_YEAR * HOURS_IN_A_DAY * MINUTES_IN_AN_HOUR * SECONDS_IN_A_MINUTE * MILLISECONDS_IN_A_SECOND)
                .isEqualTo(TimeUnit.DAYS.toMillis(365))
                .isEqualTo(TimeUnit.MILLISECONDS.convert(365, TimeUnit.DAYS))
                .isEqualTo(TimeUnit.MILLISECONDS.convert(Duration.of(365, TimeUnit.DAYS.toChronoUnit()))); // since Java 11

    }

    @Test
    void anHourInMillis() {

        long hourInMillis = TimeUnit.MILLISECONDS.convert(Duration.ofHours(1)); // since Java 11
        
        assertThat(hourInMillis)
                .isEqualTo(MINUTES_IN_AN_HOUR * SECONDS_IN_A_MINUTE * MILLISECONDS_IN_A_SECOND)
                .isEqualTo(TimeUnit.HOURS.toMillis(1))
                .isEqualTo(TimeUnit.MILLISECONDS.convert(1, TimeUnit.HOURS))
                .isEqualTo(TimeUnit.MILLISECONDS.convert(Duration.of(1, TimeUnit.HOURS.toChronoUnit()))); // since Java 11
    }

    @Test
    void aMinuteInMillis() {
        
        long minuteInMillis = TimeUnit.MILLISECONDS.convert(Duration.ofMinutes(1)); // since Java 11
        
        assertThat(minuteInMillis)
                .isEqualTo(SECONDS_IN_A_MINUTE * MILLISECONDS_IN_A_SECOND)
                .isEqualTo(TimeUnit.MINUTES.toMillis(1))
                .isEqualTo(TimeUnit.MILLISECONDS.convert(1, TimeUnit.MINUTES))
                .isEqualTo(TimeUnit.MILLISECONDS.convert(Duration.of(1, TimeUnit.MINUTES.toChronoUnit()))); // since Java 11
    }

    @ParameterizedTest
    @MethodSource("timeUnitToDuration")
    void convertTimeUnitToDuration(TimeUnit unit, Duration duration, long expectedResult) {
        long actualResult = unit.convert(duration);

        assertThat(actualResult).isEqualTo(expectedResult);
    }

    private static Stream<Arguments> timeUnitToDuration() {
        return Stream.of(
                Arguments.of(TimeUnit.DAYS, Duration.ofHours(24), 1), // 24h = 1d
                Arguments.of(TimeUnit.DAYS, Duration.ofHours(40), 1), // 40h = 1d
                Arguments.of(TimeUnit.DAYS, Duration.ofHours(48), 2), // 48h = 2d
                Arguments.of(TimeUnit.DAYS, Duration.ofHours(50), 2),  // 50h = 2d
                Arguments.of(TimeUnit.MILLISECONDS, Duration.ofSeconds(1), 1000),  // 1s = 1000ms
                Arguments.of(TimeUnit.MILLISECONDS, Duration.ofSeconds(11), 11000),  // 1s = 11000ms
                Arguments.of(TimeUnit.SECONDS, Duration.ofHours(1), 3600),  // 1h = 3600s
                Arguments.of(TimeUnit.HOURS, Duration.ofSeconds(4_000), 1),  // 4000s = 1h
                Arguments.of(TimeUnit.HOURS, Duration.ofSeconds(1_0000), 2)  // 10000s = 2h
        );
    }
}

Source code

The source code for this article can be found on Github: https://github.com/kolorobot/java9-and-beyond