Converts this Date
object to a String
of the form:
* dow mon dd hh:mm:ss zzz yyyy
where:
dow
is the day of the week ({@code Sun, Mon, Tue, Wed, Thu, Fri, Sat}).
mon
is the month ({@code Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec}).
dd
is the day of the month (01
through
31
), as two decimal digits.
hh
is the hour of the day (00
through
23
), as two decimal digits.
mm
is the minute within the hour (00
through
59
), as two decimal digits.
ss
is the second within the minute (00
through
61
, as two decimal digits.
zzz
is the time zone (and may reflect daylight saving
time). Standard time zone abbreviations include those
recognized by the method parse
. If time zone
information is not available, then zzz
is empty -
that is, it consists of no characters at all.
yyyy
is the year, as four decimal digits.
a string representation of this date.
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, theCalendar
class should be used to convert between dates and time fields and theDateFormat
class should be used to format and parse date strings. The corresponding methods inDate
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 United States Naval Observatory (USNO):
and the material regarding "Systems of Time" at:
which has descriptions of various different time systems including UT, UT1, and UTC.
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.
Author
James Gosling
Author
Arthur van Hoff
Author
Alan Liu
See
Since
1.0