Java Tutorial/Data Type/Calendar

Change multiple components at the same time

public void set (int year, int month, int date)
     public void set (int year, int month, int date, int hour, int minute, int second)

Check for a Leap Year

import java.text.ParseException;
public class MainClass {
  public static void main(String[] args) throws ParseException {
    System.out.println(isLeapYear(2000));
  }
  public static boolean isLeapYear(int year) {
    if (year < 0) {
      return false;
    }
    if (year % 400 == 0) {
      return true;
    } else if (year % 100 == 0) {
      return false;
    } else if (year % 4 == 0) {
      return true;
    } else {
      return false;
    }
  }
}

Checking for a Leap Year: using GregorianCalendar

import java.text.ParseException;
import java.util.GregorianCalendar;
public class MainClass {
  public static void main(String[] args) throws ParseException {
    System.out.println(isLeapYear(2000));
  }
  public static boolean isLeapYear(int year) {
    GregorianCalendar gcal = new GregorianCalendar();
    return gcal.isLeapYear(year);
  }
}

Construct a Calendar object by using the setTime method

import java.util.Calendar;
import java.util.Date;
public class MainClass {
  public static void main(String[] args) {
    Calendar calendar = Calendar.getInstance();
    calendar.setTime(new Date());
  }
}

Create a Date object using the Calendar class

import java.util.Calendar;
public class Main {
  public static void main(String[] args) {
    int year = 2009;
    int month = 0; // January
    int date = 1;
    Calendar cal = Calendar.getInstance();
    cal.clear();
    cal.set(Calendar.YEAR, year);
    cal.set(Calendar.MONTH, month);
    cal.set(Calendar.DATE, date);
    java.util.Date utilDate = cal.getTime();
    System.out.println(utilDate);
  }
}
//2009-01-01

Create instance of java.sql.Date from Calendar.getTimeInMillis()

import java.util.Calendar;
public class Main {
  public static void main(String[] args) {
    int year = 2009;
    int month = 0; // January
    int date = 1;
    Calendar cal = Calendar.getInstance();
    cal.clear();
    cal.set(Calendar.YEAR, year);
    cal.set(Calendar.MONTH, month);
    cal.set(Calendar.DATE, date);
    java.sql.Date sqlDate = new java.sql.Date(cal.getTimeInMillis());
    System.out.println(sqlDate);
  }
}
//2009-01-01

Display Day of Week using Java Calendar

import java.util.Calendar;
public class Main {
  public static void main(String[] args) {
    Calendar now = Calendar.getInstance();
    System.out.println("Current date : " + (now.get(Calendar.MONTH) + 1) + "-"
        + now.get(Calendar.DATE) + "-" + now.get(Calendar.YEAR));
    String[] strDays = new String[] { "Sunday", "Monday", "Tuesday", "Wednesday", "Thusday",
        "Friday", "Saturday" };
    // Day_OF_WEEK starts from 1 while array index starts from 0
    System.out.println("Current day is : " + strDays[now.get(Calendar.DAY_OF_WEEK) - 1]);
  }
}

Display full date time

import java.util.Calendar;
public class Main {
  public static void main(String[] args) {
    Calendar now = Calendar.getInstance();
    System.out.println("Current full date time is : " + (now.get(Calendar.MONTH) + 1) + "-"
        + now.get(Calendar.DATE) + "-" + now.get(Calendar.YEAR) + " "
        + now.get(Calendar.HOUR_OF_DAY) + ":" + now.get(Calendar.MINUTE) + ":"
        + now.get(Calendar.SECOND) + "." + now.get(Calendar.MILLISECOND));
  }
}

Display Month of year using Java Calendar

import java.util.Calendar;
public class Main {
  public static void main(String[] args) {
    Calendar now = Calendar.getInstance();
    System.out.println("Current date : " + (now.get(Calendar.MONTH) + 1) + "-"
        + now.get(Calendar.DATE) + "-" + now.get(Calendar.YEAR));
    String[] strMonths = new String[] { "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug",
        "Sep", "Oct", "Nov", "Dec" };
    System.out.println("Current month is : " + strMonths[now.get(Calendar.MONTH)]);
  }
}

Get current date, year and month

import java.util.Calendar;
public class Main {
  public static void main(String[] args) {
    Calendar now = Calendar.getInstance();
    // 
    System.out.println("Current Year is : " + now.get(Calendar.YEAR));
    // month start from 0 to 11
    System.out.println("Current Month is : " + (now.get(Calendar.MONTH) + 1));
    System.out.println("Current Date is : " + now.get(Calendar.DATE));
  }
}

Get current time information

import java.util.Calendar;
public class Main {
  public static void main(String[] args) {
    Calendar now = Calendar.getInstance();
    
    System.out.println("Current Hour in 12 hour format is : " + now.get(Calendar.HOUR));
    System.out.println("Current Hour in 24 hour format is : " + now.get(Calendar.HOUR_OF_DAY));
    System.out.println("Current Minute is : " + now.get(Calendar.MINUTE));
    System.out.println("Current Second is : " + now.get(Calendar.SECOND));
    System.out.println("Current Millisecond is : " + now.get(Calendar.MILLISECOND));
  }
}

Get day of week

import java.util.Calendar;
 
import java.util.Calendar;
public class Main {
  public static void main(String[] args) {
    Calendar calendar = Calendar.getInstance();
    calendar.set(Calendar.YEAR, 2007);
    calendar.set(Calendar.DAY_OF_YEAR, 180);
    // See the full information of the calendar object.
    System.out.println(calendar.getTime().toString());
    // Get the weekday and print it
    int weekday = calendar.get(Calendar.DAY_OF_WEEK);
    System.out.println("Weekday: " + weekday);
  }
}

Get Days Of The Week for different locale

import java.text.DateFormatSymbols;
import java.util.Calendar;
import java.util.Locale;
public class DaysOfTheWeek {
  public static void main(String argv[]) {
    Locale usersLocale = Locale.getDefault();
    DateFormatSymbols dfs = new DateFormatSymbols(usersLocale);
    String weekdays[] = dfs.getWeekdays();
    Calendar cal = Calendar.getInstance(usersLocale);
    int firstDayOfWeek = cal.getFirstDayOfWeek();
    int dayOfWeek;
    for (dayOfWeek = firstDayOfWeek; dayOfWeek < weekdays.length; dayOfWeek++)
      System.out.println(weekdays[dayOfWeek]);
    for (dayOfWeek = 0; dayOfWeek < firstDayOfWeek; dayOfWeek++)
      System.out.println(weekdays[dayOfWeek]);
  }
}

Get the last date of a month

import java.util.Calendar;
public class Main {
  public static void main(String[] args) {
    Calendar calendar = Calendar.getInstance();
    int lastDate = calendar.getActualMaximum(Calendar.DATE);
    System.out.println("Date     : " + calendar.getTime());
    System.out.println("Last Date: " + lastDate);
  }
}

Get the last day of a month

import java.util.Calendar;
public class Main {
  public static void main(String[] args) {
    Calendar calendar = Calendar.getInstance();
    int lastDate = calendar.getActualMaximum(Calendar.DATE);
    calendar.set(Calendar.DATE, lastDate);
    int lastDay = calendar.get(Calendar.DAY_OF_WEEK);
    System.out.println("Last Date: " + calendar.getTime());
    System.out.println("Last Day : " + lastDay);
  }
}

Get the number of days in that month

import java.util.Calendar;
public class Main {
  public static void main(String[] argv) throws Exception {
    Calendar cal = Calendar.getInstance();
    int days = cal.getActualMaximum(Calendar.DAY_OF_MONTH); // 28
  }
}

Get time in milliseconds using Java Calendar

import java.util.Calendar;
public class Main {
  public static void main(String[] args) {
    Calendar now = Calendar.getInstance();
    System.out.println("Current milliseconds since Jan 1, 1970 are :" + now.getTimeInMillis());
  }
}

Get Week of month and year using Java Calendar

import java.util.Calendar;
public class Main {
  public static void main(String[] args) {
    Calendar now = Calendar.getInstance();
    System.out.println("Current week of month is : " + now.get(Calendar.WEEK_OF_MONTH));
    System.out.println("Current week of year is : " + now.get(Calendar.WEEK_OF_YEAR));
    now.add(Calendar.WEEK_OF_MONTH, 1);
    System.out.println("date after one year : " + (now.get(Calendar.MONTH) + 1) + "-"
        + now.get(Calendar.DATE) + "-" + now.get(Calendar.YEAR));
  }
}

The java.util.Calendar Class

To create a java.util.Calendar object, you have to use its static getInstance method.

public static Calendar getInstance ()
public static Calendar getInstance (Locale locale)

To change a date/time component, use its set method: public void set (int field, int value)

import java.util.Calendar;
public class MainClass {
  public static void main(String[] args) {
    Calendar calendar = Calendar.getInstance();
    calendar.set(Calendar.MONTH, Calendar.DECEMBER);
  }
}

To obtain a date part, such as the hour, the month, or the year, use the get method

public int get (int field)

2007
0
30
8
32
42
805

Try month in a leap year

import java.util.Calendar;
import java.util.GregorianCalendar;
public class Main {
  public static void main(String[] argv) throws Exception {
    Calendar cal = new GregorianCalendar(2000, Calendar.FEBRUARY, 1);
    int days = cal.getActualMaximum(Calendar.DAY_OF_MONTH); // 29
  }
}

Using the Calendar Class to Display Current Time in Different Time Zones

import java.util.Calendar;
import java.util.TimeZone;
public class Main {
  public static void main(String[] args) {
    Calendar calNewYork = Calendar.getInstance();
    calNewYork.setTimeZone(TimeZone.getTimeZone("America/New_York"));
    System.out.println("Time in New York: " + calNewYork.get(Calendar.HOUR_OF_DAY) + ":"
        + calNewYork.get(Calendar.MINUTE));
  }
}
//Time in New York: 11:51