ChronoUnit (Java Platform SE 8 )
Keywords: java.time.temporal.ChronoUnit class
Date: 2015-11-18

compact1, compact2, compact3
java.time.temporal

## Enum ChronoUnit

- java.lang.Object
- - java.lang.Enum<ChronoUnit>
  - - java.time.temporal.ChronoUnit

- All Implemented Interfaces:
    Serializable, Comparable<ChronoUnit>, TemporalUnit

      public enum ChronoUnit
      extends Enum<ChronoUnit>
      implements TemporalUnit

  A standard set of date periods units.

  This set of units provide unit-based access to manipulate a date, time or date-time. The standard set of units can be extended by implementing `TemporalUnit`.

  These units are intended to be applicable in multiple calendar systems. For example, most non-ISO calendar systems define units of years, months and days, just with slightly different rules. The documentation of each unit explains how it operates.

  Implementation Requirements:
    This is a final, immutable and thread-safe enum.
  Since:
    1.8

- - ### Enum Constant Summary

    Enum Constants
    Enum Constant and Description
    `CENTURIES` Unit that represents the concept of a century.
    `DAYS` Unit that represents the concept of a day.
    `DECADES` Unit that represents the concept of a decade.
    `ERAS` Unit that represents the concept of an era.
    `FOREVER` Artificial unit that represents the concept of forever.
    `HALF_DAYS` Unit that represents the concept of half a day, as used in AM/PM.
    `HOURS` Unit that represents the concept of an hour.
    `MICROS` Unit that represents the concept of a microsecond.
    `MILLENNIA` Unit that represents the concept of a millennium.
    `MILLIS` Unit that represents the concept of a millisecond.
    `MINUTES` Unit that represents the concept of a minute.
    `MONTHS` Unit that represents the concept of a month.
    `NANOS` Unit that represents the concept of a nanosecond, the smallest supported unit of time.
    `SECONDS` Unit that represents the concept of a second.
    `WEEKS` Unit that represents the concept of a week.
    `YEARS` Unit that represents the concept of a year.

  - ### Method Summary

    All Methods Static Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `<R extends Temporal> R` | `addTo(R temporal, long amount)` Returns a copy of the specified temporal object with the specified period added.
    `long` | `between(Temporal temporal1Inclusive, Temporal temporal2Exclusive)` Calculates the amount of time between two temporal objects.
    `Duration` | `getDuration()` Gets the estimated duration of this unit in the ISO calendar system.
    `boolean` | `isDateBased()` Checks if this unit is a date unit.
    `boolean` | `isDurationEstimated()` Checks if the duration of the unit is an estimate.
    `boolean` | `isSupportedBy(Temporal temporal)` Checks if this unit is supported by the specified temporal object.
    `boolean` | `isTimeBased()` Checks if this unit is a time unit.
    `String` | `toString()` Returns the name of this enum constant, as contained in the declaration.
    `static ChronoUnit` | `valueOf(String name)` Returns the enum constant of this type with the specified name.
    `static ChronoUnit[]` | `values()` Returns an array containing the constants of this enum type, in the order they are declared.

    - ### Methods inherited from class java.lang.Enum

      `clone, compareTo, equals, finalize, getDeclaringClass, hashCode, name, ordinal, valueOf`

    - ### Methods inherited from class java.lang.Object

      `getClass, notify, notifyAll, wait, wait, wait`

- - ### Enum Constant Detail

    - #### NANOS

          public static final ChronoUnit NANOS

      Unit that represents the concept of a nanosecond, the smallest supported unit of time. For the ISO calendar system, it is equal to the 1,000,000,000th part of the second unit.

    - #### MICROS

          public static final ChronoUnit MICROS

      Unit that represents the concept of a microsecond. For the ISO calendar system, it is equal to the 1,000,000th part of the second unit.

    - #### MILLIS

          public static final ChronoUnit MILLIS

      Unit that represents the concept of a millisecond. For the ISO calendar system, it is equal to the 1000th part of the second unit.

    - #### SECONDS

          public static final ChronoUnit SECONDS

      Unit that represents the concept of a second. For the ISO calendar system, it is equal to the second in the SI system of units, except around a leap-second.

    - #### MINUTES

          public static final ChronoUnit MINUTES

      Unit that represents the concept of a minute. For the ISO calendar system, it is equal to 60 seconds.

    - #### HOURS

          public static final ChronoUnit HOURS

      Unit that represents the concept of an hour. For the ISO calendar system, it is equal to 60 minutes.

    - #### HALF_DAYS

          public static final ChronoUnit HALF_DAYS

      Unit that represents the concept of half a day, as used in AM/PM. For the ISO calendar system, it is equal to 12 hours.

    - #### DAYS

          public static final ChronoUnit DAYS

      Unit that represents the concept of a day. For the ISO calendar system, it is the standard day from midnight to midnight. The estimated duration of a day is `24 Hours`.

      When used with other calendar systems it must correspond to the day defined by the rising and setting of the Sun on Earth. It is not required that days begin at midnight - when converting between calendar systems, the date should be equivalent at midday.

    - #### WEEKS

          public static final ChronoUnit WEEKS

      Unit that represents the concept of a week. For the ISO calendar system, it is equal to 7 days.

      When used with other calendar systems it must correspond to an integral number of days.

    - #### MONTHS

          public static final ChronoUnit MONTHS

      Unit that represents the concept of a month. For the ISO calendar system, the length of the month varies by month-of-year. The estimated duration of a month is one twelfth of `365.2425 Days`.

      When used with other calendar systems it must correspond to an integral number of days.

    - #### YEARS

          public static final ChronoUnit YEARS

      Unit that represents the concept of a year. For the ISO calendar system, it is equal to 12 months. The estimated duration of a year is `365.2425 Days`.

      When used with other calendar systems it must correspond to an integral number of days or months roughly equal to a year defined by the passage of the Earth around the Sun.

    - #### DECADES

          public static final ChronoUnit DECADES

      Unit that represents the concept of a decade. For the ISO calendar system, it is equal to 10 years.

      When used with other calendar systems it must correspond to an integral number of days and is normally an integral number of years.

    - #### CENTURIES

          public static final ChronoUnit CENTURIES

      Unit that represents the concept of a century. For the ISO calendar system, it is equal to 100 years.

      When used with other calendar systems it must correspond to an integral number of days and is normally an integral number of years.

    - #### MILLENNIA

          public static final ChronoUnit MILLENNIA

      Unit that represents the concept of a millennium. For the ISO calendar system, it is equal to 1000 years.

      When used with other calendar systems it must correspond to an integral number of days and is normally an integral number of years.

    - #### ERAS

          public static final ChronoUnit ERAS

      Unit that represents the concept of an era. The ISO calendar system doesn't have eras thus it is impossible to add an era to a date or date-time. The estimated duration of the era is artificially defined as `1,000,000,000 Years`.

      When used with other calendar systems there are no restrictions on the unit.

    - #### FOREVER

          public static final ChronoUnit FOREVER

      Artificial unit that represents the concept of forever. This is primarily used with `TemporalField` to represent unbounded fields such as the year or era. The estimated duration of the era is artificially defined as the largest duration supported by `Duration`.

  - ### Method Detail

    - #### values

          public static ChronoUnit[] values()

      Returns an array containing the constants of this enum type, in the order they are declared. This method may be used to iterate over the constants as follows:

          for (ChronoUnit c : ChronoUnit.values())
              System.out.println(c);

      Returns:
        an array containing the constants of this enum type, in the order they are declared

    - #### valueOf

          public static ChronoUnit valueOf(String name)

      Returns the enum constant of this type with the specified name. The string must match exactly an identifier used to declare an enum constant in this type. (Extraneous whitespace characters are not permitted.)
      Parameters:
        `name` - the name of the enum constant to be returned.
      Returns:
        the enum constant with the specified name
      Throws:
        `IllegalArgumentException` - if this enum type has no constant with the specified name
        `NullPointerException` - if the argument is null

    - #### getDuration

          public Duration getDuration()

      Gets the estimated duration of this unit in the ISO calendar system.

      All of the units in this class have an estimated duration. Days vary due to daylight saving time, while months have different lengths.

      Specified by:
        `getDuration` in interface `TemporalUnit`
      Returns:
        the estimated duration of this unit, not null

    - #### isDurationEstimated

          public boolean isDurationEstimated()

      Checks if the duration of the unit is an estimate.

      All time units in this class are considered to be accurate, while all date units in this class are considered to be estimated.

      This definition ignores leap seconds, but considers that Days vary due to daylight saving time and months have different lengths.

      Specified by:
        `isDurationEstimated` in interface `TemporalUnit`
      Returns:
        true if the duration is estimated, false if accurate

    - #### isDateBased

          public boolean isDateBased()

      Checks if this unit is a date unit.

      All units from days to eras inclusive are date-based. Time-based units and `FOREVER` return false.

      Specified by:
        `isDateBased` in interface `TemporalUnit`
      Returns:
        true if a date unit, false if a time unit

    - #### isTimeBased

          public boolean isTimeBased()

      Checks if this unit is a time unit.

      All units from nanos to half-days inclusive are time-based. Date-based units and `FOREVER` return false.

      Specified by:
        `isTimeBased` in interface `TemporalUnit`
      Returns:
        true if a time unit, false if a date unit

    - #### isSupportedBy

          public boolean isSupportedBy(Temporal temporal)

      Description copied from interface: `TemporalUnit`
      Checks if this unit is supported by the specified temporal object.

      This checks that the implementing date-time can add/subtract this unit. This can be used to avoid throwing an exception.

      This default implementation derives the value using `Temporal.plus(long, TemporalUnit)`.

      Specified by:
        `isSupportedBy` in interface `TemporalUnit`
      Parameters:
        `temporal` - the temporal object to check, not null
      Returns:
        true if the unit is supported

    - #### addTo

          public <R extends Temporal> R addTo(R temporal,
                                              long amount)

      Description copied from interface: `TemporalUnit`
      Returns a copy of the specified temporal object with the specified period added.

      The period added is a multiple of this unit. For example, this method could be used to add "3 days" to a date by calling this method on the instance representing "days", passing the date and the period "3". The period to be added may be negative, which is equivalent to subtraction.

      There are two equivalent ways of using this method. The first is to invoke this method directly. The second is to use `Temporal.plus(long, TemporalUnit)`:

             // these two lines are equivalent, but the second approach is recommended
             temporal = thisUnit.addTo(temporal);
             temporal = temporal.plus(thisUnit);

      It is recommended to use the second approach, `plus(TemporalUnit)`, as it is a lot clearer to read in code.

      Implementations should perform any queries or calculations using the units available in `ChronoUnit` or the fields available in `ChronoField`. If the unit is not supported an `UnsupportedTemporalTypeException` must be thrown.

      Implementations must not alter the specified temporal object. Instead, an adjusted copy of the original must be returned. This provides equivalent, safe behavior for immutable and mutable implementations.

      Specified by:
        `addTo` in interface `TemporalUnit`
      Type Parameters:
        `R` - the type of the Temporal object
      Parameters:
        `temporal` - the temporal object to adjust, not null
        `amount` - the amount of this unit to add, positive or negative
      Returns:
        the adjusted temporal object, not null

    - #### between

          public long between(Temporal temporal1Inclusive,
                              Temporal temporal2Exclusive)

      Description copied from interface: `TemporalUnit`
      Calculates the amount of time between two temporal objects.

      This calculates the amount in terms of this unit. The start and end points are supplied as temporal objects and must be of compatible types. The implementation will convert the second type to be an instance of the first type before the calculating the amount. The result will be negative if the end is before the start. For example, the amount in hours between two temporal objects can be calculated using `HOURS.between(startTime, endTime)`.

      The calculation returns a whole number, representing the number of complete units between the two temporals. For example, the amount in hours between the times 11:30 and 13:29 will only be one hour as it is one minute short of two hours.

      There are two equivalent ways of using this method. The first is to invoke this method directly. The second is to use `Temporal.until(Temporal, TemporalUnit)`:

             // these two lines are equivalent
             between = thisUnit.between(start, end);
             between = start.until(end, thisUnit);

      The choice should be made based on which makes the code more readable.

      For example, this method allows the number of days between two dates to be calculated:

            long daysBetween = DAYS.between(start, end);
            // or alternatively
            long daysBetween = start.until(end, DAYS);

      Implementations should perform any queries or calculations using the units available in `ChronoUnit` or the fields available in `ChronoField`. If the unit is not supported an `UnsupportedTemporalTypeException` must be thrown. Implementations must not alter the specified temporal objects.

      Specified by:
        `between` in interface `TemporalUnit`
      Parameters:
        `temporal1Inclusive` - the base temporal object, not null
        `temporal2Exclusive` - the other temporal object, exclusive, not null
      Returns:
        the amount of time between temporal1Inclusive and temporal2Exclusive in terms of this unit; positive if temporal2Exclusive is later than temporal1Inclusive, negative if earlier

    - #### toString

          public String toString()

      Description copied from class: `Enum`
      Returns the name of this enum constant, as contained in the declaration. This method may be overridden, though it typically isn't necessary or desirable. An enum type should override this method when a more "programmer-friendly" string form exists.
      Specified by:
        `toString` in interface `TemporalUnit`
      Overrides:
        `toString` in class `Enum<ChronoUnit>`
      Returns:
        the name of this enum constant

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