Chapter: Java The Complete Reference - The Java Library - java.util : More Utility Classes

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Calendar - java.util

The abstract Calendar class provides a set of methods that allows you to convert a time in milliseconds to a number of useful components.

Calendar

 

The abstract Calendar class provides a set of methods that allows you to convert a time in milliseconds to a number of useful components. Some examples of the type of information that can be provided are year, month, day, hour, minute, and second. It is intended that subclasses of Calendar will provide the specific functionality to interpret time information according to their own rules. This is one aspect of the Java class library that enables you to write programs that can operate in international environments. An example of such a subclass is GregorianCalendar.

Calendar provides no public constructors. Calendar defines several protected instance variables. areFieldsSet is a boolean that indicates if the time components have been set. fields is an array of ints that holds the components of the time. isSet is a boolean array that indicates if a specific time component has been set. time is a long that holds the current time for this object. isTimeSet is a boolean that indicates if the current time has been set.

A sampling of methods defined by Calendar are shown in Table 19-5.








Calendar defines the following int constants, which are used when you get or set components of the calendar. (The ones with the suffix FORMAT or STANDALONE were added by JDK 8.)

ALL_STYLES

 

AM

 

AM_PM

 

APRIL

 

AUGUST

 

DATE

 

DAY_OF_MONTH

 

DAY_OF_WEEK

 

DAY_OF_WEEK_IN_MONTH

 

DAY_OF_YEAR

 

DECEMBER

 

DST_OFFSET

 

ERA

 

FEBRUARY

 

FIELD_COUNT

 

FRIDAY

 

HOUR

 

HOUR_OF_DAY

 

JANUARY

 

JULY

 

JUNE

 

LONG

 

LONG_FORMAT

 

LONG_STANDALONE

 

MARCH

 

MAY

 

MILLISECOND

 

MINUTE

 

MONDAY

 

MONTH

 

NARROW_FORMAT

 

NARROW_STANDALONE

 

NOVEMBER

 

OCTOBER

 

PM

 

SATURDAY

 

SECOND

 

SEPTEMBER

 

SHORT

 

SHORT_FORMAT

 

SHORT_STANDALONE

 

SUNDAY

 

THURSDAY

 

TUESDAY

 

UNDECIMBER

 

WEDNESDAY

 

WEEK_OF_MONTH

 

WEEK_OF_YEAR

 

YEAR

 

ZONE_OFFSET

 


 

The following program demonstrates several Calendar methods:

 

// Demonstrate Calendar

import java.util.Calendar;

 

class CalendarDemo {

 

public static void main(String args[]) {

String months[]   = {

"Jan",        "Feb", "Mar", "Apr",

"May",       "Jun", "Jul", "Aug",

"Sep",        "Oct", "Nov", "Dec"};

    Create a calendar initialized with the

 

    current date and time in the default

 

    locale and timezone.

 

Calendar calendar = Calendar.getInstance();

 

// Display current time and date information.

System.out.print("Date: ");

System.out.print(months[calendar.get(Calendar.MONTH)]);

System.out.print(" " + calendar.get(Calendar.DATE) + " ");

System.out.println(calendar.get(Calendar.YEAR));

System.out.print("Time: ");

 

System.out.print(calendar.get(Calendar.HOUR) + ":");

System.out.print(calendar.get(Calendar.MINUTE) + ":");

System.out.println(calendar.get(Calendar.SECOND));

// Set the time and date information and display it.

 calendar.set(Calendar.HOUR, 10);

calendar.set(Calendar.MINUTE, 29);

calendar.set(Calendar.SECOND, 22);

 System.out.print("Updated time: ");

System.out.print(calendar.get(Calendar.HOUR) + ":");

System.out.print(calendar.get(Calendar.MINUTE) + ":");

System.out.println(calendar.get(Calendar.SECOND));

 

}

 

}

 

Sample output is shown here:

 

Date: Jan 1 2014

 

Time: 11:29:39

 

Updated time: 10:29:22


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