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OCP Review 5 - Dates,strings and localization

Dates and Times in Java 8

  • LocalDate.now(): date
  • LocalTime.now(): time
  • LocalDateTime.now(): date +time
  • ZonedDateTime.now(): date + time + time zone

Current Date


LocalDate now = LocalDate.now();
System.out.println(now);

// 2015-11-08
  • LocalDate: only date (not time)
  • can’t do new LocalDate();
  • import java.time.LocalDate;

Date with year, month, day


LocalDate firstOfJanuary2015 = LocalDate.of(2015, Month.JANUARY, 1);
System.out.println(firstOfJanuary2015);

LocalDate inmutable!

LocalDate _12Oct1492_ = LocalDate.of(1492, Month.OCTOBER, 12);
_12Oct1492_.plusDays(800);
System.out.println(_12Oct1492_);								// 1492-10-12
LocalDate other = _12Oct1492_.plusDays(800);
System.out.println(other);										// 1494-12-21

LocalTime

LocalTime timeNow = LocalTime.now();
System.out.println(timeNow);									// 13:51:53.382

System.out.println(LocalTime.of(10, 10, 10));					// 10:10:10
  • LocalTime: sólo tiempo
  • LocalDateTime: fecha y hora

LocalTime inmutable!

LocalTime timeNow = LocalTime.now();
System.out.println(timeNow);

timeNow.plusHours(1);
System.out.println(timeNow);

// 19:57:24.995
// 19:57:24.995
  • plusMinutes / minusMinutes
  • plusSeconds / minus

Intervals

LocalDate start = LocalDate.of(2015, Month.APRIL, 10);
LocalDate end = LocalDate.of(2015, Month.APRIL, 20);
while (start.isBefore(end)) {
	System.out.println(start);
	start = start.plusDays(1);
}

2015-04-10
2015-04-11
2015-04-12
2015-04-13
2015-04-14
2015-04-15
2015-04-16
2015-04-17
2015-04-18
2015-04-19

Periods

  • Create task every week

Period everyWeek = Period.ofWeeks(1);
start = LocalDate.now();
end = LocalDate.of(2016, Month.APRIL, 10);
while (start.isBefore(end)) {
	System.out.println(start);
	start = start.plus(everyWeek);
}

Periods

Period.of(year, month, days)

System.out.println(Period.of(3, 2, 1));
// P3Y2M1D
// P 3Y 2M 1D

Duration

  • like Periods, but for days, hours, minutes, seconds, milliseconds, nanoseconds

Duration.ofDays()

Parse dates


DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy/MM/dd");
LocalDate date = LocalDate.parse("2010/10/40", formatter);
System.out.println(date);
  • can throw java.time.format.DateTimeParseException (Runtime)

TimeZones

System.out.println(LocalTime.now());
System.out.println(LocalTime.now(ZoneId.of("US/Pacific")));
System.out.println(LocalTime.now(ZoneId.of("Zulu")));
System.out.println(LocalTime.now(ZoneId.of("UTC")));
// console output

20:05:25.170
11:05:25.172
19:05:25.173
19:05:25.173

UTC

The official abbreviation for Coordinated Universal Time is UTC. It came about as a compromise between English and French speakers.

  • Coordinated Universal Time in English would normally be abbreviated CUT.
  • Temps Universel Coordonné in French would normally be abbreviated TUC.

GMT & UTC

Negative <– GMT 0 == UTC 0 –> Positive

LocalDateTime localDateTime = LocalDateTime.now();
System.out.println(localDateTime);

ZonedDateTime zonedDateTimeUSPacific = ZonedDateTime.now(ZoneId.of("US/Pacific"));
System.out.println(zonedDateTimeUSPacific);

ZonedDateTime zonedDateTimeMadrid = ZonedDateTime.now(ZoneId.of("Europe/Madrid"));
System.out.println(zonedDateTimeMadrid);

ZoneId.getAvailableZoneIds().stream().sorted().forEach(System.out::println);

Daylight saving time

  • last Sunday of March, we move from 1:59 AM -> 3:00 AM
LocalDate change2018 = LocalDate.of(2018, Month.MARCH, 25);
LocalTime changeTime = LocalTime.of(1, 30);
ZoneId zone = ZoneId.of("Europe/Madrid");

ZonedDateTime time = ZonedDateTime.of(change2018, changeTime, zone);

System.out.println(time); 				// 2018-03-25T01:30+01:00[Europe/Madrid]
System.out.println(time.plusHours(1));  // 2018-03-25T03:30+02:00[Europe/Madrid]
// we add 1 h, but went from 01:30 --> 03:30!

Localisation

  • You need to know how a ResourceBundle is prepared for a particular locale when multiple properties files are available. The following JavaDoc API decription contains all you need to know: http://docs.oracle.com/javase/8/docs/api/java/util/ResourceBundle.html#getBundle-java.lang.String-java.util.Locale-java.lang.ClassLoader- You may try executing the given code and see how the values are loaded. Keep the properties files in the base folder of your classpath. For example, if your classpath contains c:\javatest\classes, then keep the properties files in c:\javatest\classes.
  • Keys are always Strings. So you cannot use an int to get value for a key.

  • ResourceBundle is retrieved, changing the Locale will not affect the ResourceBundle. You have to retrieve a new ResourceBundle by passing in the new Locale and then assign it to the variable

  • EX. : mymsgs.properties is the base file for this resource bundle. Therefore, it will be loaded first. Since the language and region specific file is also present (_en_UK), it will also be loaded and the values in this file will be superimposed on the values of the base file.

      Remember that if there were another properties file named mymsgs_en.properties also present, then that file would have been loaded before mymsgs_en_UK.properties.

  • In order for a program to load a resource bundle, the resource bundle properties file must be in the CLASSPATH. The JVM attempts to find a “resource” with this name using ClassLoader.getResource. (Note that a “resource” in the sense of getResource has nothing to do with the contents of a resource bundle, it is just a container of data, such as a file.) If it finds a “resource”, it attempts to create a new PropertyResourceBundle instance from its contents. If successful, this instance becomes the result resource bundle.

  • A resource bundle file could be a properties file or a class file. The abstract class ResourceBundle has two subclasses: PropertyResourceBundle and ListResourceBundle.
    1. A PropertyResourceBundle is backed by a properties file. A properties file is a plain-text file that contains translatable text. Properties files are not part of the Java source code, and they can contain values for String objects only. If you need to store other types of objects, use a ListResourceBundle instead.
    2. The ListResourceBundle class manages resources with a convenient list. Each ListResourceBundle is backed by a class file. You can store any locale-specific object in a ListResourceBundle. To add support for an additional Locale, you create another source file and compile it into a class file. The ResourceBundle class is flexible. If you first put your locale-specific String objects in a PropertyResourceBundle and then later decided to use ListResourceBundle instead, there is no impact on your code. For example, the following call to getBundle will retrieve a ResourceBundle for the appropriate Locale, whether ButtonLabel is backed up by a class or by a properties file: ResourceBundle introLabels = ResourceBundle.getBundle(“ButtonLabel”, currentLocale);

Question

  • JavaDoc API description of the toString methods of Duration and Period.
    Duration.toString: It generates a string representation of the duration object using ISO-8601 seconds based representation, such as PT8H6M12.345S. The format of the returned string will be PTnHnMnS, where n is the relevant hours, minutes or seconds part of the duration. Any fractional seconds are placed after a decimal point i the seconds section. If a section has a zero value, it is omitted. The hours, minutes and seconds will all have the same sign. Examples:     ”20.345 seconds”                 – “PT20.345S      ”15 minutes” (15 * 60 seconds)   – “PT15M”     ”10 hours” (10 * 3600 seconds)    – “PT10H”     ”2 days” (2 * 86400 seconds)     – “PT48H”

    Note that multiples of 24 hours are not output as days to avoid confusion with Period.

    Period.toString:

    Outputs this period as a String, such as P6Y3M1D. The output will be in the ISO-8601 period format. A zero period will be represented as zero days, ‘P0D’.

  • public static Duration between(Temporal startInclusive, Temporal endExclusive)
    1. Duration.between method computes the duration between two temporal objects.  If the objects are of different types, then the duration is calculated based on the type of the first object. For example, if the first argument is a LocalTime then the second argument is converted to a LocalTime. (Not the case here because both arguments are of ZonedDateTime).
    2. In this case, the difference between the two zones is 3 hours therefore the resulting duration will contain 3 hours.
    3. The result of Duration.between method can be a negative period if the end is before the start. This is NOT the case here. Therefore, the Duration.between will return be plus 3 hrs and not minus 3 hours.
  • toString method of java.time.Duration works - It generates a string representation of the duration object using ISO-8601 seconds based representation, such as PT8H6M12.345S.
    1. Duration.between method computes the duration between two temporal objects. If the objects are of different types, then the duration is calculated based on the type of the first object. For example, in this case, since the first argument is an OffsetDateTime then the second argument will be converted to a OffsetDateTime. Now, remember that ZonedDateTime adds the functionality of Day light savings on top of OffsetDateTime. Thus, it is possible to convert a ZonedDateTime into an OffsetDateTime. The reverse is also possible. (If you try to do Duration.between(nyOdt, localDateTime);, it will throw java.time.DateTimeException: Unable to obtain ZonedDateTime from TemporalAccessor, at run time.)

  1. In this case, since DST is ON on 2nd Jun, the ZonedDateTime will be 1 hour ahead of the OffsetDateTime. Thus, the difference between the two is 1 hour.

  2. The result of Duration.between method can be a negative period if the end is before the start. This is indeed the case here. The offset of OffsetDateTime is -5, while the offset of ZonedDateTime is -4 (due to DST). Therefore, the Duration.between will return be -1H.