Problem:
How to create Java Calendar instances and display its details? In the following example we’ll show how to create Calendar in an old way and using the new Java 8 Builder.
Solution:
Basic class in Java for calculating time is java.util.Calendar. Traditionally its instances were created using getInstance factory methods, but Java 8 came with a new Calendar.Builder class that allows to set also calendar type for the new calendar.
The following program demonstrates how to create instances of Calendar class and prints some of its details:
package com.farenda.java.util;
import java.util.Calendar;
import java.util.Date;
import java.util.Locale;
import java.util.TimeZone;
public class CalendarGetInstance {
public static void main(String[] args) {
calendarWithDefaults();
calendarWithTimeZoneAndLocale();
createCalendarUsingJava8Builder();
availableCalendars();
}
private static void calendarWithDefaults() {
System.out.println("Calendar with default TimeZone and Locale");
printDetails(Calendar.getInstance());
}
private static void calendarWithTimeZoneAndLocale() {
System.out.println("Calendar with EST TimeZone and Italian Locale");
Calendar calendar = Calendar.getInstance(TimeZone.getTimeZone("EST"), Locale.ITALIAN);
printDetails(calendar);
}
private static void createCalendarUsingJava8Builder() {
System.out.println("Create using Java 8 Calendar.Builder");
printDetails(new Calendar.Builder().setCalendarType("gregory").build());
}
private static void availableCalendars() {
System.out.println("Available calendars: " + Calendar.getAvailableCalendarTypes());
for (String type : Calendar.getAvailableCalendarTypes()) {
Calendar calendar = new Calendar.Builder()
.setCalendarType(type)
.setInstant(new Date())
.build();
printDetails(calendar);
}
}
private static void printDetails(Calendar calendar) {
System.out.println("Calendar type: " + calendar.getCalendarType());
System.out.println("First day of the week: " + calendar.getFirstDayOfWeek());
System.out.println("Time since the Epoch: " + calendar.getTime());
System.out.println("Current TimeZone: " + calendar.getTimeZone().getDisplayName());
try {
System.out.println("Weeks in year: " + calendar.getWeeksInWeekYear());
} catch (UnsupportedOperationException e) {
System.out.println("Weeks in year: UnsupportedOperationException");
}
try {
System.out.println("The week year: " + calendar.getWeekYear());
} catch (UnsupportedOperationException e) {
System.out.println("The week year: UnsupportedOperationException");
}
System.out.println("As instant: " + calendar.toInstant());
System.out.println();
}
}
And here’s the result of running the above program:
Calendar with default TimeZone and Locale Calendar type: gregory First day of the week: 2 Time since the Epoch: Sun Sep 27 10:14:59 CEST 2015 Current TimeZone: Central European Time Weeks in year: 53 The week year: 2015 As instant: 2015-09-27T08:14:59.195Z Calendar with EST TimeZone and Italian Locale Calendar type: gregory First day of the week: 2 Time since the Epoch: Sun Sep 27 10:14:59 CEST 2015 Current TimeZone: Eastern Standard Time Weeks in year: 53 The week year: 2015 As instant: 2015-09-27T08:14:59.701Z Create using Java 8 Calendar.Builder Calendar type: gregory First day of the week: 2 Time since the Epoch: Thu Jan 01 00:00:00 CET 1970 Current TimeZone: Central European Time Weeks in year: 53 The week year: 1970 As instant: 1969-12-31T23:00:00Z Available calendars: [gregory, buddhist, japanese] Calendar type: gregory First day of the week: 2 Time since the Epoch: Sun Sep 27 10:14:59 CEST 2015 Current TimeZone: Central European Time Weeks in year: 53 The week year: 2015 As instant: 2015-09-27T08:14:59.706Z Calendar type: buddhist First day of the week: 2 Time since the Epoch: Sun Sep 27 10:14:59 CEST 2015 Current TimeZone: Central European Time Weeks in year: 53 The week year: 2558 As instant: 2015-09-27T08:14:59.711Z Calendar type: japanese First day of the week: 2 Time since the Epoch: Sun Sep 27 10:14:59 CEST 2015 Current TimeZone: Central European Time Weeks in year: UnsupportedOperationException The week year: UnsupportedOperationException As instant: 2015-09-27T08:14:59.724Z
As you can see there are 3 types of Calendar on my system: gregory, buddhist, japanese. Each of them calculates time differently.
Another thing to note is that Calendar created with Calendar.getInstance() Factory Method is initialized with current time, but the one created with Calendar.Builder has to have time set explicitly.
