Java - Legacy Date Time Classes

  1. HOME
  2. Java
  3. Date Time
  4. Legacy Date Time Classes

Introduction

The main legacy classes are Date, Calendar, and GregorianCalendar which are in the java.util package.

Date Class

Date class represents an instant in time.

A Date object stores the number of milliseconds elapsed since the epoch, midnight January 1, 1970 UTC.

The default constructor of the Date class is used to create a Date object with the current system datetime.

The following code shows how to use Date class.

Demo

import java.util.Date;

public class Main {
  public static void main(String[] args) {
    // Create a new Date object
    Date currentDate = new Date();
    System.out.println("Current date: " + currentDate);

    // Get the milliseconds value of the current date
    long millis = currentDate.getTime();
    System.out.println("Current datetime in millis: " + millis);
  }/*from   ww  w .  j  a  v a 2 s  . co  m*/
}

Result

Date object works with a 1900-based year.

Calendar Class

Calendar is an abstract class. The GregorianCalendar class is a concrete class, which inherits the Calendar class.

Calendar class declares some final static fields to represent date fields.

Calendar.JANUARY can be used to specify the January month in a date.

GregorianCalendar class has a default constructor, which create an object to represent the current datetime.

Demo

import java.util.Calendar;
import java.util.GregorianCalendar;
import java.util.TimeZone;

public class Main {
  public static void main(String[] args) {

    // Get the current date in the system default time zone
    GregorianCalendar currentDate = new GregorianCalendar();

    // Get GregorianCalendar object representing March 26, 2018 06:30:45 AM
    GregorianCalendar someDate = new GregorianCalendar(2018, Calendar.MARCH,
        26, 6, 30, 45);/*  w w  w.  j ava 2 s .c  o m*/

    // Get Indian time zone, which is GMT+05:30
    TimeZone indianTZ = TimeZone.getTimeZone("GMT+05:30");

    // Get current date in India
    GregorianCalendar indianDate = new GregorianCalendar(indianTZ);

    // Get Moscow time zone, which is GMT+03:00
    TimeZone moscowTZ = TimeZone.getTimeZone("GMT+03:00");

    // Get current date in Moscow
    GregorianCalendar moscowDate = new GregorianCalendar(moscowTZ);
  }
}

The month part of a date ranges from 0 to 11. That is, January is 0, February is 1, and so on.

You should use Calendar.JANUARY constant to represent the January month in your program instead of a 0.

Demo

import java.util.Calendar;
import java.util.GregorianCalendar;

public class Main {
  public static void main(String[] args) {
    // Create a GregorianCalendar object
    GregorianCalendar gc = new GregorianCalendar();

    // year will contain the current year value
    int year = gc.get(Calendar.YEAR);

    // month will contain the current month value
    int month = gc.get(Calendar.MONTH);

    // day will contain day of month of the current date
    int day = gc.get(Calendar.DAY_OF_MONTH);

    // hour will contain hour value
    int hour = gc.get(Calendar.HOUR);

    // minute will contain minute value
    int minute = gc.get(Calendar.MINUTE);

    // second will contain second values
    int second = gc.get(Calendar.SECOND);
  }//  w w  w.  ja  v  a 2  s  . co  m
}

The following code illustrates the use of some of the methods of the GregorianCalendar class.

Demo

import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;

public class Main {
  public static void main(String[] args) {
    GregorianCalendar gc = new GregorianCalendar();
    System.out.println("Current Date: " + getStr(gc));

    // Add 1 year
    gc.add(Calendar.YEAR, 1);/*from ww  w.j ava  2 s  .c o m*/
    System.out.println("After adding a year: " + getStr(gc));

    // Add 15 days
    gc.add(Calendar.DATE, 15);
    System.out.println("After adding 15 days: " + getStr(gc));

    long millis = gc.getTimeInMillis();
    Date dt = gc.getTime();
    System.out.println("Time in millis: " + millis);
    System.out.println("Time as Date: " + dt);
  }

  public static String getStr(GregorianCalendar gc) {
    int day = gc.get(Calendar.DAY_OF_MONTH);
    int month = gc.get(Calendar.MONTH);
    int year = gc.get(Calendar.YEAR);
    int hour = gc.get(Calendar.HOUR);
    int minute = gc.get(Calendar.MINUTE);
    int second = gc.get(Calendar.SECOND);

    String str = day + "/" + (month + 1) + "/" + year + " " + hour + ":"
        + minute + ":" + second;
    return str;
  }
}

Result

Related Topics

Exercise