public class Date extends Object implements Serializable, Cloneable, Comparable<Date>
Date represents a specific instant in time, with millisecond precision.
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:
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.
Calendar,
TimeZone,
Serialized Form| Constructor and Description |
|---|
Date()
Allocates a
Date object and initializes it so that it represents the time at
which it was allocated, measured to the nearest millisecond. |
Date(long date)
Allocates a
Date object and initializes it to represent the specified number of
milliseconds since the standard base time known as "the epoch", namely January 1, 1970,
00:00:00 GMT. |
| Modifier and Type | Method and Description |
|---|---|
boolean |
after(Date when)
Tests if this date is after the specified date.
|
boolean |
before(Date when)
Tests if this date is before the specified date.
|
Object |
clone()
Return a copy of this object.
|
int |
compareTo(Date anotherDate)
Compares two Dates for ordering.
|
boolean |
equals(Object obj)
Compares two dates for equality.
|
long |
getTime()
Returns the number of milliseconds since January 1, 1970, 00:00:00 GMT represented by this
Date object.
|
int |
hashCode()
Returns a hash code value for this object.
|
void |
setTime(long time)
Sets this
Date object to represent a point in time that is time
milliseconds after January 1, 1970 00:00:00 GMT. |
String |
toString()
Converts this
Date object to a String of the form: |
public Date()
Date object and initializes it so that it represents the time at
which it was allocated, measured to the nearest millisecond.System.currentTimeMillis()public Date(long date)
Date object and initializes it to represent the specified number of
milliseconds since the standard base time known as "the epoch", namely January 1, 1970,
00:00:00 GMT.date - the milliseconds since January 1, 1970, 00:00:00 GMT.System.currentTimeMillis()public boolean after(Date when)
when - a date.true if and only if the instant represented by this Date object
is strictly later than the instant represented by when; false
otherwise.NullPointerException - if when is null.public boolean before(Date when)
when - a date.true if and only if the instant of time represented by this
Date object is strictly earlier than the instant represented by
when; false otherwise.NullPointerException - if when is null.public Object clone()
public int compareTo(Date anotherDate)
compareTo in interface Comparable<Date>anotherDate - the Date to be compared.0 if the argument Date is equal to this Date; a value less
than 0 if this Date is before the Date argument; and a value greater
than 0 if this Date is after the Date argument.NullPointerException - if anotherDate is null.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.
public long getTime()
public int hashCode()
getTime() method. That is,
the hash code is the value of the expression: (int) (this.getTime() ˆ (this.getTime() >>> 32))
hashCode in class ObjectObject.equals(java.lang.Object),
System.identityHashCode(java.lang.Object)public void setTime(long time)
Date object to represent a point in time that is time
milliseconds after January 1, 1970 00:00:00 GMT.time - the number of milliseconds.public String toString()
Date object to a String of the form: where:dow mon dd hh:mm:ss zzz yyyy