Java Date Time Tutorial with Examples

package org.o7planning.tutorial.dt;

public class JobTimeDemo {

	// This is the method to sum the numbers from 1 to 100.
	private static int sum() {
		int sum = 0;
		for (int i = 0; i <= 100; i++) {
			sum += i;
		}
		return sum;
	}

	private static void doJob(int count) {
		// Invoke 'sum' method with the number of times
		// given by the parameter.
		for (int i = 0; i < count; i++) {
			sum();
		}
	}

	public static void main(String[] args) {
		long millis1 = System.currentTimeMillis();

		doJob(10000);

		long millis2 = System.currentTimeMillis();

		long distance = millis2 - millis1;

		System.out.println("Distance time in milli second: " + distance);
	}
}

// Number of minutes.
int minute = 5;

// Convert to milliseconds.
// This is the traditional way.
int millisecond = minute * 60 * 1000;

// Using TimeUnit:
long millisecond = TimeUnit.MINUTES.toMillis(minute);

// Convert to nanoseconds.
public long toNanos(long d);

// Convert to microseconds.
public long toMicros(long d);

// Convert to milliseconds.
public long toMillis(long d);

// Convert to seconds.
public long toSeconds(long d);

// Convert to minutes.
public long toMinutes(long d);

// Convert to hours.
public long toHours(long d);

// Convert to days.
public long toDays(long d) ;

// Convert to another time unit, given by the parameter 'u'.
public long convert(long d, TimeUnit u);

package org.o7planning.tutorial.timeunit;

import java.util.concurrent.TimeUnit;

public class TimeUnitConvertDemo {

	public static void main(String[] args) {

		// Second.
		long second = 125553;

		// Convert the number of seconds above to minutes.
		long minute = TimeUnit.MINUTES.convert(second, TimeUnit.SECONDS);
		System.out.println("Minute " + minute);

		// Convert the number of seconds above to hours.
		long hour = TimeUnit.HOURS.convert(second, TimeUnit.SECONDS);
		System.out.println("Hour " + hour);

		System.out.println("------");

		// Convert 3 days to minutes
		minute = TimeUnit.DAYS.toMinutes(3);

		System.out.println("Minute " + minute);

		// Convert 3 days to hours
		hour = TimeUnit.DAYS.toHours(3);

		System.out.println("Hour " + hour);
	}

}

// Create a Date object describing the current time.
Date date1 = new Date();

// Create a Date object, 
// millis - the milliseconds since January 1, 1970, 00:00:00 GMT.
long millis = .....;
Date date2 = new Date(millis);

package org.o7planning.tutorial.date;

import java.util.Date;
import java.util.concurrent.TimeUnit;

public class DateDemo {

	public static void main(String[] args) throws InterruptedException {

		// Create a Date object describing the current time.
		Date date1 = new Date();

		// Stop 3 seconds.
		Thread.sleep(TimeUnit.SECONDS.toMillis(3));

		// Returns the current time in milliseconds.
		// (From 01-01-1970 to now).
		long millis = System.currentTimeMillis();
		Date date2 = new Date(millis);

		// Compare two objects date1 and date2.
		// i < 0 means date1 < date2
		// i = 0 means date1 = date2
		// i > 0 means date1 > date2
		int i = date1.compareTo(date2);

		System.out.println("date1 compareTo date2 = " + i);

		// Tests if this date is before the specified date.
		boolean before = date1.before(date2);

		System.out.println("date1 before date2 ? " + before);

		// Tests if this date is after the specified date.
		boolean after = date1.after(date2);

		System.out.println("date1 after date2 ? " + after);
	}

}

public static Calendar getInstance();

public static Calendar getInstance(TimeZone zone);

public static Calendar getInstance(Locale aLocale);

public static Calendar getInstance(TimeZone zone,Locale aLocale);

// Create Calendar object describes the present time.
// With default Locale, and default TimeZone.
// (Of running computer).
Calendar c = Calendar.getInstance();

/**
* Gets a calendar using the default time zone and locale. The
* <code>Calendar</code> returned is based on the current time
* in the default time zone with the default locale.
*
* @return a Calendar.
*/
public static Calendar getInstance()
{
  Calendar cal = createCalendar(TimeZone.getDefaultRef(),
                                  Locale.getDefault(Locale.Category.FORMAT));
  cal.sharedZone = true;
  return cal;
}

/**
* Gets a calendar using the specified time zone and default locale.
* The <code>Calendar</code> returned is based on the current time
* in the given time zone with the default locale.
*
* @param zone the time zone to use
* @return a Calendar.
*/
public static Calendar getInstance(TimeZone zone)
{
  return createCalendar(zone, Locale.getDefault(Locale.Category.FORMAT));
}

/**
* Gets a calendar using the default time zone and specified locale.
* The <code>Calendar</code> returned is based on the current time
* in the default time zone with the given locale.
*
* @param aLocale the locale for the week data
* @return a Calendar.
*/
public static Calendar getInstance(Locale aLocale)
{
  Calendar cal = createCalendar(TimeZone.getDefaultRef(), aLocale);
  cal.sharedZone = true;
  return cal;
}

/**
* Gets a calendar with the specified time zone and locale.
* The <code>Calendar</code> returned is based on the current time
* in the given time zone with the given locale.
*
* @param zone the time zone to use
* @param aLocale the locale for the week data
* @return a Calendar.
*/
public static Calendar getInstance(TimeZone zone,
                                 Locale aLocale)
{
  return createCalendar(zone, aLocale);
}

private static Calendar createCalendar(TimeZone zone,
                                     Locale aLocale)
{
  Calendar cal = null;

  String caltype = aLocale.getUnicodeLocaleType("ca");
  if (caltype == null) {
      // Calendar type is not specified.
      // If the specified locale is a Thai locale,
      // returns a BuddhistCalendar instance.
      if ("th".equals(aLocale.getLanguage())
              && ("TH".equals(aLocale.getCountry()))) {
          cal = new BuddhistCalendar(zone, aLocale);
      } else {
          cal = new GregorianCalendar(zone, aLocale);
      }
  } else if (caltype.equals("japanese")) {
      cal = new JapaneseImperialCalendar(zone, aLocale);
  } else if (caltype.equals("buddhist")) {
      cal = new BuddhistCalendar(zone, aLocale);
  } else {
      // Unsupported calendar type.
      // Use Gregorian calendar as a fallback.
      cal = new GregorianCalendar(zone, aLocale);
  }

  return cal;
}

package org.o7planning.tutorial.calendar;

import java.util.Calendar;

public class CalendarFieldsDemo {

	public static void main(String[] args) {
		// Create a calendar using the default time zone and locale.
		Calendar c = Calendar.getInstance();
		int year = c.get(Calendar.YEAR);

		// Returns value from 0 - 11
		int month = c.get(Calendar.MONTH);
		int day = c.get(Calendar.DAY_OF_MONTH);
		int hour = c.get(Calendar.HOUR_OF_DAY);
		int minute = c.get(Calendar.MINUTE);
		int second = c.get(Calendar.SECOND);
		int millis = c.get(Calendar.MILLISECOND);

		System.out.println("Year: " + year);
		System.out.println("Month: " + (month + 1));
		System.out.println("Day: " + day);
		System.out.println("Hour: " + hour);
		System.out.println("Minute: " + minute);
		System.out.println("Second: " + second);
		System.out.println("Minute: " + minute);
		System.out.println("Milli Second: " + millis);

	}

}

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

// Adds or subtracts the specified amount of time to the given calendar field.
// Based on the calendar's rules.
void add(int field, int amount)

// Roll (up/down) a field of Calendar.
// roll(): Does not affect other fields of Calendar.
void roll(int calendarField, boolean up)

// Roll up a field of Calendar.
// roll(): Does not affect other fields of Calendar.
void roll(int calendarField, int amount):

// Returns a Date object based on values of Calendar.
Date getTime()

void setTime(Date date)

// Return number of milliseconds of this Calendar.
long getTimeInMills():

void setTimeInMillis(long millis)

void setTimeZone(TimeZone value)

package org.o7planning.tutorial.calendar;

import java.util.Calendar;

public class CalendarDemo {

	public static void showCalendar(Calendar c) {
		int year = c.get(Calendar.YEAR);

		// Return value from 0 - 11
		int month = c.get(Calendar.MONTH);
		int day = c.get(Calendar.DAY_OF_MONTH);
		int hour = c.get(Calendar.HOUR_OF_DAY);
		int minute = c.get(Calendar.MINUTE);
		int second = c.get(Calendar.SECOND);
		int millis = c.get(Calendar.MILLISECOND);

		System.out.println(" " + year + "-" + (month + 1) + "-" + day //
				+ " " + hour + ":" + minute + ":" + second + " " + millis);
	}

	public static void main(String[] args) {
		// Create a calendar using the default time zone and locale
		Calendar c = Calendar.getInstance();

		System.out.println("First calendar info");
		showCalendar(c);

		// roll(..): Roll a field of Calendar.
		// roll(..): Does not change other fields.
		// Example: Roll up one hour (boolean up = true)
		c.roll(Calendar.HOUR_OF_DAY, true);

		System.out.println("After roll 1 hour");
		showCalendar(c);

		// roll(..): Does not change other fields.
		// Roll down one hour (boolean up = false)
		c.roll(Calendar.HOUR_OF_DAY, false);

		System.out.println("After roll -1 hour");
		showCalendar(c);

		// add(..): Can change other fields of Calendar.
		// Adding one hour (boolean up = true)
		c.add(Calendar.HOUR_OF_DAY, 1);

		System.out.println("After add 1 hour");
		showCalendar(c);

		// roll(..): Does not change other fields of Calendar.
		// Roll down 30 day (boolean up = false)
		c.roll(Calendar.DAY_OF_MONTH, -30);

		System.out.println("After roll -30 day");
		showCalendar(c);

		// add(..): Can change other fields of Calendar.
		// Adding 30 days (boolean up = true)
		c.add(Calendar.DAY_OF_MONTH, 30);
		System.out.println("After add 30 day");
		showCalendar(c);

	}

}

Date now = new Date();

Calendar c = Calendar.getInstance();
c.setTime(now);

Calendar c = Calendar.getInstance();

Date date = c.getTime();

package org.o7planning.tutorial.calendar;

import java.util.Calendar;
import java.util.Date;
import java.util.concurrent.TimeUnit;

public class CalendarDateConversionDemo {

	public static void showCalendar(Calendar c) {
		int year = c.get(Calendar.YEAR);

		// Returns the value from 0-11
		int month = c.get(Calendar.MONTH);
		int day = c.get(Calendar.DAY_OF_MONTH);
		int hour = c.get(Calendar.HOUR_OF_DAY);
		int minute = c.get(Calendar.MINUTE);
		int second = c.get(Calendar.SECOND);
		int millis = c.get(Calendar.MILLISECOND);

		System.out.println(year + "-" + (month + 1) + "-" + day //
				+ " " + hour + ":" + minute + ":" + second + " " + millis);
	}

	public static void main(String[] args) {

		Calendar c = Calendar.getInstance();

		// year, month, day
		c.set(2000, 11, 24);

		Date date = c.getTime();

		System.out.println("Date " + date);

		long timeInMillis = System.currentTimeMillis();

		// Subtract 24 hours
		timeInMillis -= TimeUnit.HOURS.toMillis(24);

		Date date2 = new Date(timeInMillis);
		Calendar c2 = Calendar.getInstance();
		c2.setTime(date2);

		showCalendar(c2);

	}

}

Date date = new Date();

DateFormat df = new SimpleDateFormat("dd-MM-yyyy HH:mm:ss");

String dateString  = df.format(date);

String dateString = "23/04/2005 23:11:59";

DateFormat df = new SimpleDateFormat("dd/MM/yyyy HH:mm:ss");

Date date = df.parse(dateString);

package org.o7planning.tutorial.dateformat;

import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

public class DateFormatDemo {

  public static void main(String[] args) throws ParseException {

      final DateFormat df1 = new SimpleDateFormat("dd/MM/yyyy HH:mm:ss");

      String dateString1 = "23/04/2005 23:11:59";
      System.out.println("dateString1 = " + dateString1);

      // String ==> Date
      Date date1 = df1.parse(dateString1);

      System.out.println("date1 = " + date1);

      final DateFormat df2 = new SimpleDateFormat("dd-MM-yyyy HH:mm:ss");

      // Date ==> String.
      String dateString2 = df2.format(date1);

      System.out.println("dateString2 = " + dateString2);
  }
}