Java date class parse

Содержание

Class Date
Constructor Summary
Parsing and Formatting
Parsing
Formatting
Java date class parse
Constructor Summary

Class Date

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 United States Naval Observatory (USNO):

and the material regarding «Systems of Time» at:

which has descriptions of various different time systems including UT, UT1, and UTC.

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.

Constructor Summary

Allocates a Date object and initializes it so that it represents the time at which it was allocated, measured to the nearest millisecond.

As of JDK version 1.1, replaced by Calendar.set(year + 1900, month, date) or GregorianCalendar(year + 1900, month, date) .

Parsing and Formatting

The temporal-based classes in the Date-Time API provide parse methods for parsing a string that contains date and time information. These classes also provide format methods for formatting temporal-based objects for display. In both cases, the process is similar: you provide a pattern to the DateTimeFormatter to create a formatter object. This formatter is then passed to the parse or format method.

The DateTimeFormatter class provides numerous predefined formatters, or you can define your own.

The parse and the format methods throw an exception if a problem occurs during the conversion process. Therefore, your parse code should catch the DateTimeParseException error and your format code should catch the DateTimeException error. For more information on exception handing, see Catching and Handling Exceptions.

The DateTimeFormatter class is both immutable and thread-safe; it can (and should) be assigned to a static constant where appropriate.

Version Note: The java.time date-time objects can be used directly with java.util.Formatter and String.format by using the familiar pattern-based formatting that was used with the legacy java.util.Date and java.util.Calendar classes.

Parsing

The one-argument parse(CharSequence) method in the LocalDate class uses the ISO_LOCAL_DATE formatter. To specify a different formatter, you can use the two-argument parse(CharSequence, DateTimeFormatter) method. The following example uses the predefined BASIC_ISO_DATE formatter, which uses the format 19590709 for July 9, 1959.

String in = . ; LocalDate date = LocalDate.parse(in, DateTimeFormatter.BASIC_ISO_DATE);

You can also define a formatter using your own pattern. The following code, from the Parse example, creates a formatter that applies a format of «MMM d yyyy». This format specifies three characters to represent the month, one digit to represent day of the month, and four digits to represent the year. A formatter created using this pattern would recognize strings such as «Jan 3 2003» or «Mar 23 1994». However, to specify the format as «MMM dd yyyy», with two characters for day of the month, then you would have to always use two characters, padding with a zero for a one-digit date: «Jun 03 2003».

String input = . ; try < DateTimeFormatter formatter = DateTimeFormatter.ofPattern("MMM d yyyy"); LocalDate date = LocalDate.parse(input, formatter); System.out.printf("%s%n", date); >catch (DateTimeParseException exc) < System.out.printf("%s is not parsable!%n", input); throw exc; // Rethrow the exception. >// 'date' has been successfully parsed

The documentation for the DateTimeFormatter class specifies the full list of symbols that you can use to specify a pattern for formatting or parsing.

The StringConverter example on the Non-ISO Date Conversion page provides another example of a date formatter.

Formatting

The format(DateTimeFormatter) method converts a temporal-based object to a string representation using the specified format. The following code, from the Flight example, converts an instance of ZonedDateTime using the format «MMM d yyy hh:mm a». The date is defined in the same manner as was used for the previous parsing example, but this pattern also includes the hour, minutes, and a.m. and p.m. components.

ZoneId leavingZone = . ; ZonedDateTime departure = . ; try < DateTimeFormatter format = DateTimeFormatter.ofPattern("MMM d yyyy hh:mm a"); String out = departure.format(format); System.out.printf("LEAVING: %s (%s)%n", out, leavingZone); >catch (DateTimeException exc)

The output for this example, which prints both the arrival and departure time, is as follows:

LEAVING: Jul 20 2013 07:30 PM (America/Los_Angeles) ARRIVING: Jul 21 2013 10:20 PM (Asia/Tokyo)

Источник

Java date class parse

The class 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 × 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 United States Naval Observatory (USNO):

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.

Constructor Summary

Allocates a Date object and initializes it so that it represents the time at which it was allocated, measured to the nearest millisecond.

As of JDK version 1.1, replaced by Calendar.set(year + 1900, month, date) or GregorianCalendar(year + 1900, month, date) .

As of JDK version 1.1, replaced by Calendar.set(year + 1900, month, date, hrs, min) or GregorianCalendar(year + 1900, month, date, hrs, min) .

As of JDK version 1.1, replaced by Calendar.set(year + 1900, month, date, hrs, min, sec) or GregorianCalendar(year + 1900, month, date, hrs, min, sec) .

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.

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