Legacy Calendar
Description
Calendar is an abstract class. GregorianCalendar class extends Calendar class.
Constructor
The GregorianCalendar class has a default constructor, which create an object to represent the current datetime.
GregorianCalendar class also defines constructors we can use to create a specific date.
We can also create date in a particular time zone.
import java.util.Calendar;
import java.util.GregorianCalendar;
import java.util.TimeZone;
// ww w . j av a 2 s .c o m
public class Main {
public static void main(String[] args) {
// Get the current date in the system default time zone
GregorianCalendar currentDate = new GregorianCalendar();
System.out.println(currentDate.getTime());
// Get GregorianCalendar object representing March 21, 2014 07:30:45 AM
GregorianCalendar someDate = new GregorianCalendar(2014, Calendar.MARCH,
21, 7, 30, 45);
System.out.println(someDate.getTime());
// Get Indian time zone, which is GMT+05:30
TimeZone indianTZ = TimeZone.getTimeZone("GMT+05:30");
GregorianCalendar indianDate = new GregorianCalendar(indianTZ);
System.out.println(indianDate.getTime());
}
}
The code above generates the following result.
Field
The month part of a date ranges from 0 to 11. January is 0, February is 1, and so on.
get() with requested field returns the value of a field in a datetime.
import java.util.Calendar;
import java.util.GregorianCalendar;
//from w w w. ja v a2s. c o m
public class Main {
public static void main(String[] args) {
GregorianCalendar gc = new GregorianCalendar();
// current year value
int year = gc.get(Calendar.YEAR);
System.out.println(year);
// current month value
int month = gc.get(Calendar.MONTH);
System.out.println(month);
// day of month
int day = gc.get(Calendar.DAY_OF_MONTH);
System.out.println(day);
// hour value
int hour = gc.get(Calendar.HOUR);
System.out.println(hour);
// minute value
int minute = gc.get(Calendar.MINUTE);
System.out.println(minute);
// second values
int second = gc.get(Calendar.SECOND);
System.out.println(second);
}
}
The code above generates the following result.
add()
add() adds an value to a date.
The amount may be negative or positive. The Calendar knows how to
adjust.
import java.util.Calendar;
import java.util.GregorianCalendar;
// ww w.j av a 2 s. c o m
public class Main {
public static void main(String[] args) {
GregorianCalendar gc = new GregorianCalendar(2014, Calendar.DECEMBER, 1);
gc.add(Calendar.MONTH, 5);
System.out.println(gc.getTime());
}
}
The code above generates the following result.
roll()
roll() adds a amount to the specified calendar field without changing larger fields.
It is an overloaded method.
void roll(int field, int amount)
void roll(int field, boolean up)
Suppose we have a GregorianCalendar set to August 31, 1999.
Calling roll(Calendar.MONTH, 8) sets the calendar to April 30, 1999.
DAY_OF_MONTH field cannot be 31 in the month April.
DAY_OF_MONTH is set to the closest possible value,
30. The YEAR field maintains the value of 1999 because it is a
larger field than MONTH.
roll(Calendar.MONTH, 1) is the same as roll(Calendar. MONTH, true).
roll(Calendar.MONTH, -1) is the same as roll(Calendar.MONTH, false).
import java.util.Calendar;
import java.util.GregorianCalendar;
/* ww w . ja va2 s . co m*/
public class Main {
public static void main(String[] args) {
GregorianCalendar gc = new GregorianCalendar();
System.out.println("Current Date: " + gc.getTime());
// Add 1 year
gc.add(Calendar.YEAR, 1);
System.out.println(gc.getTime());
// Add 15 days
gc.add(Calendar.DATE, 15);
System.out.println(gc.getTime());
}
}