Previous
Java API
Index
Next
| Package java.util |
Previous |
Java API |
Index |
Next |
public class java.util.Date
extends java.lang.Object
{
// Constructors
public Date();
public Date(int year, int month, int date);
public Date(int year, int month, int date,
int hrs, int min);
public Date(int year, int month, int date,
int hrs, int min, int sec);
public Date(long date);
public Date(String s);
// Methods
public boolean after(Date when);
public boolean before(Date when);
public boolean equals(Object obj);
public int getDate();
public int getDay();
public int getHours();
public int getMinutes();
public int getMonth();
public int getSeconds();
public long getTime();
public int getTimezoneOffset();
public int getYear();
public int hashCode();
public static long parse(String s);
public void setDate(int date);
public void setHours(int hours);
public void setMinutes(int minutes);
public void setMonth(int month);
public void setSeconds(int seconds);
public void setTime(long time);
public void setYear(int year);
public String toGMTString();
public String toLocaleString();
public String toString();
public static long UTC(int year, int month, int date,
int hrs, int min, int sec);
}
The class Date provides anabstraction of dates and times. Dates may be constructed from a year, month, date (day of month), hour, minute, and second. Those six components, as well as the day of the week, may be extracted from a date. Dates may also be compared and converted to a readable string form. A date is represented to a precision of one millisecond.
To print today's date:
System.out.println("today = " + new Date());
To find out the day of the week for some particular date, for example, January 16, 1963:
new Date(63, 0, 16).getDay()
While the Date class is intended to reflect UTC (Coordinated Universal Time), 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 GMT (Greenwich Mean Time), which is equivalent to UT (Universal Time). 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 GPS (the satellite-based Global Positioning System) is synchronized to UTC but is not adjusted for leap seconds. An interesting source of further information is the US 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:
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.
public Date()Allocates a Date object and initializes it so that it represents the time at which it was allocated measured to the nearest millisecond.
See Also: currentTimeMillis in class System.
public Date(int year, int month, int date)Allocates a 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.
Parameter Description year the year minus 1900 month a month between 0-11 date day of the month between 1-31
public Date(int year, int month, int date, int hrs, int min)Allocates a Date object and initializes it so that it represents the specified hour and minute, local time, of the date specified by the year, month, and date arguments.
Parameter Description year the year minus 1900 month a month between 0-11 date day of the month between 1-31 hrs hours between 0-23 min minutes between 0-59
public Date(int year, int month, int date, int hrs, int min, int sec)Allocates a 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, and date arguments.
Parameter Description year the year minus 1900 month a month between 0-11 date day of the month between 1-31 hrs hours between 0-23 min minutes between 0-59 sec seconds between 0-59
public Date(long date)Allocates a Date object and initializes it to represent the specified number of milliseconds since January 1, 1970, 00:00:00GMT.
Parameter Description date milliseconds since January 1, 1970, 00:00:00 GMT See Also: currentTimeMillis in class System.
public Date(String s)Allocates a Date object and initializes it that that it represents the date and time indicated by the string s, which is interpreted as if by the parse method .
Parameter Description s a string representation of the date.
public boolean after(Date when)Return Value:
Returns true if this date is after the argument date; false otherwise.
Parameter Description when a date
public boolean before(Date when)Return Value:
Returns true if this date is before the argument date; false otherwise.
Parameter Description when a date
public boolean equals(Object obj)The result is 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.
Return Value:
Returns true if the objects are the same; false otherwise.
Parameter Description obj the object to compare with Overrides:
equals in class Object .
public int getDate()Return Value:
Returns the day of the month represented by this date. The value returned is between 1 and 31.
public int getDay()Return Value:
Returns the day of the week represented by this date. The value returned is between 0 and 6, where 0 represents Sunday.
public int getHours()Return Value:
Returns the hour represented by this date. The value returned is between 0 and 23, where 0 represents midnight.
public int getMinutes()Return Value:
Returns the number of minutes past the hour represented by this date. The value returned is between 0 and 59.
public int getMonth()Return Value:
Returns the month represented by this date. The value returned is between 0 and 11, with the value 0 representing January.
public int getSeconds()Return Value:
Returns the number of seconds past the minute represented by this date. The value returned is between 0 and 60. The value 60 can only occur on those Java Virtual Machines that take leap seconds into account.
public long getTime()Return Value:
Returns the number of milliseconds since January 1, 1970, 00:00:00 GMT represented by this date.
public int getTimezoneOffset()Determines the local time zone offset. The time zone noffset is the number of minutes that must be added to Greenwich Mean Time to give the local time zone. This value includes the correction, if necessary, for daylight savings time.
Return Value:
Returns the time zone offset, in minutes, for the current locale.
public int getYear()Return Value:
Returns the year represented by this date, minus 1900.
public int hashCode()Return Value:
Returns a hash code value for this object.
Overrides:
hashCode in class Object .
public static long parse(String s)Given a string representing a time, parse it and return the time value. This method recognizes most standard syntaxes.
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 US time zone abbreviations, but for general use, a timezone 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.
Return Value:
Returns the number of milliseconds since January 1, 1970, 00:00:00 GMT represented by the string argument
Parameter Description s a string to be parsed as a date
public void setDate(int date)Sets the day of the month of this date to the specified value
Parameter Description date the day value
public void setHours(int hours)Sets the hour of this date to the specified value
Parameter Description hours the hour value
public void setMinutes(int minutes)Sets the minutes of this date to the specified value
Parameter Description minutes the value of the minutes
public void setMonth(int month)Sets the month of this date to the specified value.
Parameter Description month the month value (0-11)
public void setSeconds(int seconds)Sets the seconds of this date to the specified value.
Parameter Description seconds the second value
public void setTime(long time)Sets this date to represent the specified number of milliseconds since January 1, 1970 00:00:00 GMT.
Parameter Description time A number of milliseconds
public void setYear(int year)Sets the year of this date to be the specified value plus 1900.
Parameter Description year the year value
public String toGMTString()Creates a string representation of this date. The result is of the form
"12 Aug 1995 02:30:00 GMT"the day of the month is always one or two digits. The other fields have exactly the width shown. The timezone is always given as "GMT".
Return Value:
Returns A string represention of this date, using the Internet GMT conventions.
public String toLocaleString()Creates a string representation of this date is an implementation-dependent form. The intent is that the form should be familiar to the user of the Java application, wherever it may happen to be running. The intent is comparible to that of the %c format supported by the strftime() function of ISO C.
Return Value:
Returns A string representation of this date, using the locale conventions.
public String toString()Creates a canonical string representation of the date. The result is of the form "Sat Aug 12 02:30:00 PDT 1995".
Return Value:
Returns A string representation of this date.
Overrides:
toString in class Object .
public static longUTC(int year, int month, int date, int hrs, int min, int sec)Determines the date and time based on the arguments. The arguments are interpreted in UTC, not in the local time zone.
Return Value:
Returns the number of seconds since January 1, 1970, 00:00:00 GMT for the date and time specified by the arguments.
Parameter Description year the year minus 1900 month a month between 0-11 date day of the month between 1-31 hrs hours between 0-23 min minutes between 0-59 sec seconds between 0-59
© 1996 Sun Microsystems, Inc. All rights reserved.