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§3.2 Class Date

public  class  java.util.Date
    extends  java.lang.Object  (I-§1.12)
{
        // Constructors
    public Date();	§3.2.1
    public Date(int  year, int  month, int  date);	§3.2.2
    public Date(int  year, int  month, int  date,	§3.2.3
                            int  hrs, int  min);
    public Date(int  year, int  month, int  date,	§3.2.4
                            int  hrs, int  min, int  sec);
    public Date(long  date);	§3.2.5
    public Date(String  s);	§3.2.6

        // Methods
    public boolean after(Date  when);	§3.2.7
    public boolean before(Date  when);	§3.2.8
    public boolean equals(Object  obj);	§3.2.9
    public int getDate();	§3.2.10
    public int getDay();	§3.2.11
    public int getHours();	§3.2.12
    public int getMinutes();	§3.2.13
    public int getMonth();	§3.2.14
    public int getSeconds();	§3.2.15
    public long getTime();	§3.2.16
    public int getTimezoneOffset();	§3.2.17
    public int getYear();	§3.2.18
    public int hashCode();	§3.2.19
    public static long parse(String  s);	§3.2.20
    public void setDate(int  date);	§3.2.21
    public void setHours(int  hours);	§3.2.22
    public void setMinutes(int  minutes);	§3.2.23
    public void setMonth(int  month);	§3.2.24
    public void setSeconds(int  seconds);	§3.2.25
    public void setTime(long  time);	§3.2.26
    public void setYear(int  year);	§3.2.27
    public String toGMTString();	§3.2.28
    public String toLocaleString();	§3.2.29
    public String toString();	§3.2.30
    public static long UTC(int  year, int  month, int  date,	§3.2.31
                                        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 =

= 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:

A year is represented by the integer .
A month is represented by an integer form 0 to 11; 0 is January, 1 is February, and so on; 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 AM is hour 0, and the hour from noon to 1 PM 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 60; the value 60 occurs only for leap seconds and even then only in Java implementations that actually track leap seconds correctly.

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

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 (I-§1.18.5) in class System.

Date

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.

Parameters:: year -the year minus 1900; month -a month between 0-11; date -day of the month between 1-31

Date

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.

Parameters:: 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

Date

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.

Parameters:: 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

Date

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.

Parameters:: date -milliseconds since January 1, 1970, 00:00:00 GMT
See Also:: currentTimeMillis (I-§1.18.5) in class System.

Date

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 (I-§3.2.20).

Parameters:: s -a string representation of the date.

after

public boolean after(Date  when)

Parameters:: when -a date
Returns:: true if this date is after the argument date; false otherwise.

before

public boolean before(Date  when)

Parameters:: when -a date
Returns:: true if this date is before the argument date; false otherwise.

equals

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 (I-§3.2.16) returns the same long value for both.

Parameters:: obj -the object to compare with
Returns:: true if the objects are the same; false otherwise.
Overrides:: equals in class Object (I-§1.12.3).

getDate

public int getDate()

Returns:: the day of the month represented by this date. The value returned is between 1 and 31.

getDay

public int getDay()

Returns:: the day of the week represented by this date. The value returned is between 0 and 6, where 0 represents Sunday.

getHours

public int getHours()

Returns:: the hour represented by this date. The value returned is between 0 and 23, where 0 represents midnight.

getMinutes

public int getMinutes()

Returns:: the number of minutes past the hour represented by this date. The value returned is between 0 and 59.

getMonth

public int getMonth()

Returns:: the month represented by this date. The value returned is between 0 and 11, with the value 0 representing January.

getSeconds

public int getSeconds()

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.

getTime

public long getTime()

Returns:: the number of milliseconds since January 1, 1970, 00:00:00 GMT represented by this date.

getTimezoneOffset

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.

Returns:: the time zone offset, in minutes, for the current locale.

getYear

public int getYear()

Returns:: the year represented by this date, minus 1900.

hashCode

public int hashCode()

Returns:: a hash code value for this object.
Overrides:: hashCode in class Object (I-§1.12.6).

parse

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.

Parameters:: s -a string to be parsed as a date
Returns:: the number of milliseconds since January 1, 1970, 00:00:00 GMT represented by the string argument

setDate

public void setDate(int  date)

Sets the day of the month of this date to the specified value

Parameters:: date -the day value

setHours

public void setHours(int  hours)

Sets the hour of this date to the specified value

Parameters:: hours -the hour value

setMinutes

public void setMinutes(int  minutes)

Sets the minutes of this date to the specified value

Parameters:: minutes -the value of the minutes

setMonth

public void setMonth(int  month)

Sets the month of this date to the specified value.

Parameters:: month -the month value (0-11)

setSeconds

public void setSeconds(int  seconds)

Sets the seconds of this date to the specified value.

Parameters:: seconds -the second value

setTime

public void setTime(long  time)

Sets this date to represent the specified number of milliseconds since January 1, 1970 00:00:00 GMT.

Parameters:: time -A number of milliseconds

setYear

public void setYear(int  year)

Sets the year of this date to be the specified value plus 1900.

Parameters:: year -the year value

toGMTString

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".

Returns:: A string represention of this date, using the Internet GMT conventions.

toLocaleString

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.

Returns:: A string representation of this date, using the locale conventions.

toString

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".
Returns:: A string representation of this date.
Overrides:: toString in class Object (I-§1.12.9).

UTC

public static long

UTC(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.

Parameters:: 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
Returns:: the number of seconds since January 1, 1970, 00:00:00 GMT for the date and time specified by the arguments.

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