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java.lang.Object
|
+----java.util.Date
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 ю 60 ю 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:
http://tycho.usno.navy.mil
and their definitions of "Systems of Time" at:
http://tycho.usno.navy.mil/systime.html
In all methods of class Date that 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.
Date()
Date object and initializes it so that
it represents the time at which it was allocated measured to the
nearest millisecond.
Date(int, int, int)
Date object and initializes it so that
it represents midnight, local time, at the beginning of the day
specified by the year, month, and
date arguments.
Deprecated.
Date(int, int, int, int, int)
Date object and initializes it so that
it represents the specified hour and minute, local time, of the
date specified by the year, month,
date, hrs, and min arguments.
Deprecated.
Date(int, int, int, int, int, int)
Date object and initializes it so that
it represents the specified hour, minute, and second, local time
of the date specified by the year, month,
date, hrs, min, and
sec arguments.
Deprecated.
Date(long)
Date object and initializes it to
represent the specified number of milliseconds since January 1,
1970, 00:00:00 GMT.
Date(String)
Date object and initializes it so that
it represents the date and time indicated by the string
s, which is interpreted as if by the
parse method.
Deprecated.
after(Date)
before(Date)
equals(Object)
getDate()
getDay()
getHours()
getMinutes()
getMonth()
getSeconds()
getTime()
getTimezoneOffset()
getYear()
hashCode()
parse(String)
setDate(int)
setHours(int)
setMinutes(int)
setMonth(int)
setSeconds(int)
setTime(long)
setYear(int)
toGMTString()
toLocaleString()
toString()
UTC(int, int, int, int, int, int)
Date
public Date()
Date object and initializes it so that
it represents the time at which it was allocated measured to the
nearest millisecond.
Date
public Date(long date)
Date object and initializes it to
represent the specified number of milliseconds since January 1,
1970, 00:00:00 GMT.
Date
public Date(int year,
int month,
int date)
Date object and initializes it so that
it represents midnight, local time, at the beginning of the day
specified by the year, month, and
date arguments.
Date
public Date(int year,
int month,
int date,
int hrs,
int min)
Date object and initializes it so that
it represents the specified hour and minute, local time, of the
date specified by the year, month,
date, hrs, and min arguments.
Date
public Date(int year,
int month,
int date,
int hrs,
int min,
int sec)
Date object and initializes it so that
it represents the specified hour, minute, and second, local time
of the date specified by the year, month,
date, hrs, min, and
sec arguments.
Date
public Date(String s)
Date object and initializes it so that
it represents the date and time indicated by the string
s, which is interpreted as if by the
parse method.
UTC
public static long UTC(int year,
int month,
int date,
int hrs,
int min,
int sec)
parse
public static long parse(String s)
It accepts many syntaxes; in particular, it recognizes the IETF standard date syntax: "Sat, 12 Aug 1995 13:30:00 GMT". It also understands the continental U.S. time-zone abbreviations, but for general use, a time-zone offset should be used: "Sat, 12 Aug 1995 13:30:00 GMT+0430" (4 hours, 30 minutes west of the Greenwich meridian). If no time zone is specified, the local time zone is assumed. GMT and UTC are considered equivalent.
getYear
public int getYear()
setYear
public void setYear(int year)
getMonth
public int getMonth()
0 and 11, with the value
0 representing January.
setMonth
public void setMonth(int month)
getDate
public int getDate()
1 and 31.
setDate
public void setDate(int date)
getDay
public int getDay()
0 and 6, where 0
represents Sunday.
getHours
public int getHours()
0 and 23, where 0 represents
midnight.
setHours
public void setHours(int hours)
getMinutes
public int getMinutes()
0 and 59.
setMinutes
public void setMinutes(int minutes)
getSeconds
public int getSeconds()
0 and 60. The
value 60 can only occur on those Java Virtual Machines that
take leap seconds into account.
setSeconds
public void setSeconds(int seconds)
getTime
public long getTime()
setTime
public void setTime(long time)
before
public boolean before(Date when)
true if this date is before the argument date;
false otherwise.
after
public boolean after(Date when)
true if this date is after the argument date;
false otherwise.
equals
public boolean equals(Object obj)
true if and only if the argument is
not null and is a Date object that
represents the same point in time, to the millisecond, as this object.
Thus, two Date objects are equal if and only if the
getTime method returns the same long
value for both.
true if the objects are the same;
false otherwise.
hashCode
public int hashCode()
toString
public String toString()
"Sat Aug 12 02:30:00 PDT 1995".
toLocaleString
public String toLocaleString()
%c" format supported by the strftime()
function of ISO C.
toGMTString
public String toGMTString()
"12 Aug 1995 02:30:00 GMT"
in which the day of the month is always one or two digits. The other fields have exactly the width shown. The time zone is always given as "GMT".
getTimezoneOffset
public int getTimezoneOffset()
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