The class Date represents a specific instant
in time, with millisecond precision.
Prior to JDK 1.1, the class Date had two additional
functions. It allowed the interpretation of dates as year, month, day, hour,
minute, and second values. It also allowed the formatting and parsing
of date strings. Unfortunately, the API for these functions was not
amenable to internationalization. As of JDK 1.1, the
Calendar class should be used to convert between dates and time
fields and the DateFormat class should be used to format and
parse date strings.
The corresponding methods in Date are deprecated.
Although the Date class is intended to reflect
coordinated universal time (UTC), it may not do so exactly,
depending on the host environment of the Java Virtual Machine.
Nearly all modern operating systems assume that 1 day =
24 × 60 × 60 = 86400 seconds
in all cases. In UTC, however, about once every year or two there
is an extra second, called a "leap second." The leap
second is always added as the last second of the day, and always
on December 31 or June 30. For example, the last minute of the
year 1995 was 61 seconds long, thanks to an added leap second.
Most computer clocks are not accurate enough to be able to reflect
the leap-second distinction.
Some computer standards are defined in terms of Greenwich mean
time (GMT), which is equivalent to universal time (UT). GMT is
the "civil" name for the standard; UT is the
"scientific" name for the same standard. The
distinction between UTC and UT is that UTC is based on an atomic
clock and UT is based on astronomical observations, which for all
practical purposes is an invisibly fine hair to split. Because the
earth's rotation is not uniform (it slows down and speeds up
in complicated ways), UT does not always flow uniformly. Leap
seconds are introduced as needed into UTC so as to keep UTC within
0.9 seconds of UT1, which is a version of UT with certain
corrections applied. There are other time and date systems as
well; for example, the time scale used by the satellite-based
global positioning system (GPS) is synchronized to UTC but is
not adjusted for leap seconds. An interesting source of
further information is the U.S. Naval Observatory, particularly
the Directorate of Time at:
In all methods of class Date that accept or return
year, month, date, hours, minutes, and seconds values, the
following representations are used:
A year y is represented by the integer
y- 1900.
A month is represented by an integer from 0 to 11; 0 is January,
1 is February, and so forth; thus 11 is December.
A date (day of month) is represented by an integer from 1 to 31
in the usual manner.
An hour is represented by an integer from 0 to 23. Thus, the hour
from midnight to 1 a.m. is hour 0, and the hour from noon to 1
p.m. is hour 12.
A minute is represented by an integer from 0 to 59 in the usual manner.
A second is represented by an integer from 0 to 61; the values 60 and
61 occur only for leap seconds and even then only in Java
implementations that actually track leap seconds correctly. Because
of the manner in which leap seconds are currently introduced, it is
extremely unlikely that two leap seconds will occur in the same
minute, but this specification follows the date and time conventions
for ISO C.
In all cases, arguments given to methods for these purposes need
not fall within the indicated ranges; for example, a date may be
specified as January 32 and is interpreted as meaning February 1.
Daterepresents a specific instant in time, with millisecond precision.Prior to JDK 1.1, the class
Datehad two additional functions. It allowed the interpretation of dates as year, month, day, hour, minute, and second values. It also allowed the formatting and parsing of date strings. Unfortunately, the API for these functions was not amenable to internationalization. As of JDK 1.1, theCalendarclass should be used to convert between dates and time fields and theDateFormatclass should be used to format and parse date strings. The corresponding methods inDateare deprecated.Although the
Dateclass is intended to reflect coordinated universal time (UTC), it may not do so exactly, depending on the host environment of the Java Virtual Machine. Nearly all modern operating systems assume that 1 day = 24 × 60 × 60 = 86400 seconds in all cases. In UTC, however, about once every year or two there is an extra second, called a "leap second." The leap second is always added as the last second of the day, and always on December 31 or June 30. For example, the last minute of the year 1995 was 61 seconds long, thanks to an added leap second. Most computer clocks are not accurate enough to be able to reflect the leap-second distinction.Some computer standards are defined in terms of Greenwich mean time (GMT), which is equivalent to universal time (UT). GMT is the "civil" name for the standard; UT is the "scientific" name for the same standard. The distinction between UTC and UT is that UTC is based on an atomic clock and UT is based on astronomical observations, which for all practical purposes is an invisibly fine hair to split. Because the earth's rotation is not uniform (it slows down and speeds up in complicated ways), UT does not always flow uniformly. Leap seconds are introduced as needed into UTC so as to keep UTC within 0.9 seconds of UT1, which is a version of UT with certain corrections applied. There are other time and date systems as well; for example, the time scale used by the satellite-based global positioning system (GPS) is synchronized to UTC but is not adjusted for leap seconds. An interesting source of further information is the U.S. Naval Observatory, particularly the Directorate of Time at:
and their definitions of "Systems of Time" at:
In all methods of class
Datethat accept or return year, month, date, hours, minutes, and seconds values, the following representations are used:- 1900.In all cases, arguments given to methods for these purposes need not fall within the indicated ranges; for example, a date may be specified as January 32 and is interpreted as meaning February 1.