Java Tutorial/Data Type/Gregorian Calendar

Calendar.DAY_OF_WEEK

import java.util.Calendar;
import java.util.GregorianCalendar;
public class MainClass {
  public static void main(String[] a) {
    GregorianCalendar calendar = new GregorianCalendar();
    calendar.set(Calendar.DAY_OF_WEEK, Calendar.TUESDAY);
  }
}

Comparing Calendars

import java.util.Calendar;
import java.util.GregorianCalendar;
public class MainClass {
  public static void main(String[] a) {
    GregorianCalendar today = new GregorianCalendar();
    GregorianCalendar thisDate = new GregorianCalendar();
    thisDate.set(Calendar.YEAR, 2000);
    if (thisDate.before(today)) {
      System.out.println("before");
    }
    if (today.after(thisDate)) {
      System.out.println("after");
    }
  }
}

Creating a Calendar object from a locale

import java.util.GregorianCalendar;
import java.util.Locale;
public class MainClass {
  public static void main(String[] a) {
    GregorianCalendar calendar = new GregorianCalendar(Locale.UK);
  }
}

Creating a Date Object for a Particular Date

import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;
public class Main {
  public static void main(String[] argv) throws Exception {
    Calendar xmas = new GregorianCalendar(1998, Calendar.DECEMBER, 25);
    Date date = xmas.getTime();
  }
}

Creating Gregorian Calendars

import java.util.Date;
import java.util.GregorianCalendar;
public class MainClass {
  public static void main(String[] a) {
    GregorianCalendar calendar = new GregorianCalendar();
    Date now = calendar.getTime();
    System.out.println(now);
  }
}

Tue Jan 16 10:06:13 PST 2007

Determine the day of the week

import java.util.Calendar;
import java.util.GregorianCalendar;
public class Main {
  public static void main(String[] argv) throws Exception {
    GregorianCalendar newCal = new GregorianCalendar();
    int day = newCal.get(Calendar.DAY_OF_WEEK);
    newCal = new GregorianCalendar();
    newCal.set(1997, 2, 1, 0, 0, 0);
    newCal.setTime(newCal.getTime());
    day = newCal.get(Calendar.DAY_OF_WEEK);
  }
}

Displaying Date by weekday name

import static java.util.Calendar.DATE;
import static java.util.Calendar.DAY_OF_WEEK;
import static java.util.Calendar.MONTH;
import static java.util.Calendar.YEAR;
import java.text.DateFormatSymbols;
import java.util.GregorianCalendar;
public class MainClass {
  public static void main(String[] args) {
    GregorianCalendar birthdate = new GregorianCalendar(1999, 1, 1);
    GregorianCalendar today = new GregorianCalendar(); // Today"s date
    GregorianCalendar birthday = new GregorianCalendar(today.get(YEAR), birthdate.get(MONTH),
        birthdate.get(DATE));
    int age = today.get(today.YEAR) - birthdate.get(YEAR);
    String[] weekdays = new DateFormatSymbols().getWeekdays(); // Get day names
    System.out.println("You were born on a " + weekdays[birthdate.get(DAY_OF_WEEK)]);
    System.out.println("This year you " + (birthday.after(today) ? " will be " : "are ") + age
        + " years old.");
    System.out.println("In " + today.get(YEAR) + " your birthday "
        + (today.before(birthday) ? "will be" : "was") + " on a "
        + weekdays[birthday.get(DAY_OF_WEEK)] + ".");
  }
}

You were born on a Monday
This year you  will be 8 years old.
In 2007 your birthday will be on a Thursday.

Getting Date and Time Information: get the day of the week

import java.util.Calendar;
import java.util.GregorianCalendar;
public class MainClass {
  public static void main(String[] a) {
    GregorianCalendar calendar = new GregorianCalendar();
    calendar.set(Calendar.DAY_OF_WEEK, Calendar.TUESDAY);
    int day = calendar.get(Calendar.DAY_OF_WEEK);
    System.out.println(day);
  }
}

Integer constants for the third version of set()

FieldValueAM_PMAM or PMDAY_OF_WEEKSUNDAY, MONDAY..., through to SATURDAYDAY_OF_YEARSet a value from 1 to 366MONTHSet a value of JANUARY, FEBRUARY, etc., through to DECEMBER, corresponding to values of 0 to 11DAY_OF_MONTH or DATESet a value from 1 to 31WEEK_OF_MONTHSet a value from 1 to 6WEEK_OF_YEARSet a value from 1 to 54HOUR_OF_DAYA value from 0 to 23HOURA value from 1 to 12 representing the current hour in the a.m. or p.m.MINUTEThe current minute in the current hour � a value from 0 to 59SECONDThe second in the current minute, 0 to 59MILLISECONDThe millisecond in the current second, 0 to 999YEARThe current year � for example, 2004ERACan be set to either GregorianCalendar.BC or GregorianCalendar.AD (both values being defined in the GregorianCalendar class)ZONE_OFFSETA millisecond value indicating the offset from GMTDST_OFFSETA millisecond value indicating the offset for daylight saving time in the current time zone

Modifying Dates and Times: adding 14 to the year

import java.util.Calendar;
import java.util.GregorianCalendar;
public class MainClass {
  public static void main(String[] a) {
    GregorianCalendar calendar = new GregorianCalendar();
    calendar.set(Calendar.DAY_OF_WEEK, Calendar.TUESDAY);
    calendar.add(Calendar.YEAR, 14); // 14 years into the future
    System.out.println(calendar.get(Calendar.YEAR));
  }
}

2021

Printing out weekday names

import java.text.DateFormatSymbols;
public class MainClass {
  public static void main(String[] args) {
    String[] weekdays = new DateFormatSymbols().getWeekdays(); // Get day names
    for(String s: weekdays){
      System.out.println(s);
    }
  }
}

Sunday
Monday
Tuesday
Wednesday
Thursday
Friday
Saturday

Setting a GregorianCalendar object to a particular date

import java.util.GregorianCalendar;
public class MainClass {
  public static void main(String[] a) {
    GregorianCalendar calendar = new GregorianCalendar();
    calendar.set(1995, 10, 29); // Date set to 29th November 1999
  }
}

Setting the Date and Time

import java.util.Date;
import java.util.GregorianCalendar;
public class MainClass {
  public static void main(String[] a) {
    Date date = new Date();
    GregorianCalendar calendar = new GregorianCalendar();
    calendar.setTime(date);
  }
}

Set with GregorianCalendar.YEAR, MONTH and DATE

import java.util.GregorianCalendar;
public class Main {
  public static void main(String[] argv) throws Exception {
    GregorianCalendar gc = new GregorianCalendar();
    gc.setLenient(false);
    gc.set(GregorianCalendar.YEAR, 2003);
    gc.set(GregorianCalendar.MONTH, 12);
    gc.set(GregorianCalendar.DATE, 1);
    gc.getTime();
  }
}

Specifying the locale(TimeZone) explicitly for Gregorian Calendar

import java.util.GregorianCalendar;
import java.util.Locale;
import java.util.TimeZone;
public class MainClass {
  public static void main(String[] a) {
    GregorianCalendar calendar = new GregorianCalendar(TimeZone.getTimeZone("America/Chicago"),
        Locale.US);
    System.out.println(calendar);
  }
}

To go into the past: making the second argument negative in the "add" method

import java.util.Calendar;
import java.util.GregorianCalendar;
public class MainClass {
  public static void main(String[] a) {
    GregorianCalendar calendar = new GregorianCalendar();
    calendar.set(Calendar.DAY_OF_WEEK, Calendar.TUESDAY);
    calendar.add(Calendar.YEAR, -14); 
    System.out.println(calendar.get(Calendar.YEAR));
  }
}

1993

To increment or decrement a field of a calendar by 1 using the roll() method

By +1 or -1, depending on the second argument(true or false).

import java.util.Calendar;
import java.util.GregorianCalendar;
public class MainClass {
  public static void main(String[] a) {
    GregorianCalendar calendar = new GregorianCalendar();
    calendar.roll(Calendar.MONTH, false); // Go back a month
    System.out.println(calendar.get(Calendar.MONTH));
  }
}

11

Using a switch statement on the values for day

import java.util.Calendar;
import java.util.GregorianCalendar;
public class MainClass {
  public static void main(String[] a) {
    GregorianCalendar calendar = new GregorianCalendar();
    calendar.set(Calendar.DAY_OF_WEEK, Calendar.TUESDAY);
    int day = calendar.get(Calendar.DAY_OF_WEEK);
    switch (day) {
    case Calendar.MONDAY:
      System.out.println(Calendar.MONDAY);
      break;
    case Calendar.TUESDAY:
      System.out.println(Calendar.TUESDAY);
      break;
    default:  
      System.out.println("others");
    }
  }
}