Java Doc for Date.java in  » 6.0-JDK-Core » Collections-Jar-Zip-Logging-regex » java » util » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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 × 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:

• 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
version:
   1.90, 05/05/07
See Also:   java.text.DateFormat
See Also:   java.util.Calendar
See Also:   java.util.TimeZone
since:
   JDK1.0

Thus, two Date objects are equal if and only if the getTime method returns the same long value for both.

 dow mon dd hh:mm:ss zzz yyyy

• dow is the day of the week (Sun, Mon, Tue, Wed, Thu, Fri, Sat).
• mon is the month (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).

Thus, two Date objects are equal if and only if the getTime method returns the same long value for both.
Parameters:
  obj - the object to compare with. true if the objects are the same;false otherwise.
See Also:   java.util.Date.getTime

For example, in Massachusetts, five time zones west of Greenwich:

 new Date(96, 1, 14).getTimezoneOffset() returns 300

 new Date(96, 5, 1).getTimezoneOffset() returns 240

This method produces the same result as if it computed:

 (this.getTime() - UTC(this.getYear(), 
 this.getMonth(), 
 this.getDate(),
 this.getHours(), 
 this.getMinutes(), 
 this.getSeconds())) / (60 * 1000)
 

 (int)(this.getTime()^(this.getTime() >>> 32))

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.

The string s is processed from left to right, looking for data of interest. Any material in s that is within the ASCII parenthesis characters ( and ) is ignored. Parentheses may be nested. Otherwise, the only characters permitted within s are these ASCII characters:

 abcdefghijklmnopqrstuvwxyz
 ABCDEFGHIJKLMNOPQRSTUVWXYZ
 0123456789,+-:/

A consecutive sequence of decimal digits is treated as a decimal number:

• If a number is preceded by + or - and a year has already been recognized, then the number is a time-zone offset. If the number is less than 24, it is an offset measured in hours. Otherwise, it is regarded as an offset in minutes, expressed in 24-hour time format without punctuation. A preceding - means a westward offset. Time zone offsets are always relative to UTC (Greenwich). Thus, for example, -5 occurring in the string would mean "five hours west of Greenwich" and +0430 would mean "four hours and thirty minutes east of Greenwich." It is permitted for the string to specify GMT, UT, or UTC redundantly-for example, GMT-5 or utc+0430.
• The number is regarded as a year number if one of the following conditions is true:
  • The number is equal to or greater than 70 and followed by a space, comma, slash, or end of string
  • The number is less than 70, and both a month and a day of the month have already been recognized
  If the recognized year number is less than 100, it is interpreted as an abbreviated year relative to a century of which dates are within 80 years before and 19 years after the time when the Date class is initialized. After adjusting the year number, 1900 is subtracted from it. For example, if the current year is 1999 then years in the range 19 to 99 are assumed to mean 1919 to 1999, while years from 0 to 18 are assumed to mean 2000 to 2018. Note that this is slightly different from the interpretation of years less than 100 that is used in java.text.SimpleDateFormat .
• If the number is followed by a colon, it is regarded as an hour, unless an hour has already been recognized, in which case it is regarded as a minute.
• If the number is followed by a slash, it is regarded as a month (it is decreased by 1 to produce a number in the range 0 to 11), unless a month has already been recognized, in which case it is regarded as a day of the month.
• If the number is followed by whitespace, a comma, a hyphen, or end of string, then if an hour has been recognized but not a minute, it is regarded as a minute; otherwise, if a minute has been recognized but not a second, it is regarded as a second; otherwise, it is regarded as a day of the month.

A consecutive sequence of letters is regarded as a word and treated as follows:

• A word that matches AM, ignoring case, is ignored (but the parse fails if an hour has not been recognized or is less than 1 or greater than 12).
• A word that matches PM, ignoring case, adds 12 to the hour (but the parse fails if an hour has not been recognized or is less than 1 or greater than 12).
• Any word that matches any prefix of SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, or SATURDAY, ignoring case, is ignored. For example, sat, Friday, TUE, and Thurs are ignored.
• Otherwise, any word that matches any prefix of JANUARY, FEBRUARY, MARCH, APRIL, MAY, JUNE, JULY, AUGUST, SEPTEMBER, OCTOBER, NOVEMBER, or DECEMBER, ignoring case, and considering them in the order given here, is recognized as specifying a month and is converted to a number (0 to 11). For example, aug, Sept, april, and NOV are recognized as months. So is Ma, which is recognized as MARCH, not MAY.
• Any word that matches GMT, UT, or UTC, ignoring case, is treated as referring to UTC.
• Any word that matches EST, CST, MST, or PST, ignoring case, is recognized as referring to the time zone in North America that is five, six, seven, or eight hours west of Greenwich, respectively. Any word that matches EDT, CDT, MDT, or PDT, ignoring case, is recognized as referring to the same time zone, respectively, during daylight saving time.

Once the entire string s has been scanned, it is converted to a time result in one of two ways. If a time zone or time-zone offset has been recognized, then the year, month, day of month, hour, minute, and second are interpreted in UTC and then the time-zone offset is applied. Otherwise, the year, month, day of month, hour, minute, and second are interpreted in the local time zone.
Parameters:
  s - a string to be parsed as a date. the number of milliseconds since January 1, 1970, 00:00:00 GMTrepresented by the string argument.
See Also:   java.text.DateFormat

 dow mon dd hh:mm:ss zzz yyyy

• dow is the day of the week (Sun, Mon, Tue, Wed, Thu, Fri, Sat).
• mon is the month (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.