Java - Date and Time

Java provides the Date class available in java.util package, this class encapsulates the current date and time.

The Date class supports two constructors as shown in the following table.

Following are the methods of the date class.

Getting Current Date and Time

This is a very easy method to get current date and time in Java. You can use a simple Date object with toString() method to print the current date and time as follows −

Example

import java.util.Date;

public class DateDemo {

  public static void main(String args[]) {

     // Instantiate a Date object

     Date date = new Date();

     // display time and date using toString()

     System.out.println(date.toString());

  }

}

This will produce the following result −

Output

on May 04 09:51:52 CDT 2009

Date Comparison

Following are the three ways to compare two dates −

·        You can use getTime( ) to obtain the number of milliseconds that have elapsed since midnight, January 1, 1970, for both objects and then compare these two values.

·        You can use the methods before( ), after( ), and equals( ). Because the 12th of the month comes before the 18th, for example, new Date(99, 2, 12).before(new Date (99, 2, 18)) returns true.

·        You can use the compareTo( ) method, which is defined by the Comparable interface and implemented by Date.

Date Formatting Using SimpleDateFormat

SimpleDateFormat is a concrete class for formatting and parsing dates in a locale-sensitive manner. SimpleDateFormat allows you to start by choosing any user-defined patterns for date-time formatting.

Example

import java.util.*;

import java.text.*;

public class DateDemo {

  public static void main(String args[]) {

     Date dNow = new Date( );

     SimpleDateFormat ft =

     new SimpleDateFormat ("E yyyy.MM.dd 'at' hh:mm:ss a zzz");

     System.out.println("Current Date: " + ft.format(dNow));

  }

}

This will produce the following result −

Output

Current Date: Sun 2004.07.18 at 04:14:09 PM PDT

Simple DateFormat Format Codes

To specify the time format, use a time pattern string. In this pattern, all ASCII letters are reserved as pattern letters, which are defined as the following −

Date Formatting Using printf

Date and time formatting can be done very easily using printf method. You use a two-letter format, starting with t and ending in one of the letters of the table as shown in the following code.

Example

import java.util.Date;

import java.util.Date;

public class DateDemo {

  public static void main(String args[]) {

     // Instantiate a Date object

     Date date = new Date();

     // display time and date using toString()

     String str = String.format("Current Date/Time : %tc", date );

     System.out.printf(str);

  }

}

This will produce the following result −

Output

Current Date/Time : Sat Dec 15 16:37:57 MST 2012

It would be a bit silly if you had to supply the date multiple times to format each part. For that reason, a format string can indicate the index of the argument to be formatted.

The index must immediately follow the % and it must be terminated by a $.

Example

import java.util.Date;

public class DateDemo {

  public static void main(String args[]) {

     // Instantiate a Date object

     Date date = new Date();

     // display time and date using toString()

     System.out.printf("%1$s %2$tB %2$td, %2$tY", "Due date:", date);

  }

}

This will produce the following result −

Output

Due date: February 09, 2004

Alternatively, you can use the < flag. It indicates that the same argument as in the preceding format specification should be used again.

Example

import java.util.Date;

public class DateDemo {

  public static void main(String args[]) {

     // Instantiate a Date object

     Date date = new Date();

     // display formatted date

     System.out.printf("%s %tB %<te, %<tY", "Due date:", date);

  }

}

This will produce the following result −

Output

Due date: February 09, 2004

Date and Time Conversion Characters

There are other useful classes related to Date and time. For more details, you can refer to Java Standard documentation.

Parsing Strings into Dates

The SimpleDateFormat class has some additional methods, notably parse( ), which tries to parse a string according to the format stored in the given SimpleDateFormat object.

Example

import java.util.*;

import java.text.*;

public class DateDemo {

  public static void main(String args[]) {

     SimpleDateFormat ft = new SimpleDateFormat ("yyyy-MM-dd");

     String input = args.length == 0 ? "1818-11-11" : args[0];

     System.out.print(input + " Parses as ");

     Date t;

     try {

        t = ft.parse(input);

        System.out.println(t);

     }catch (ParseException e) {

        System.out.println("Unparseable using " + ft);

     }

  }

}

A sample run of the above program would produce the following result −

Output

1818-11-11 Parses as Wed Nov 11 00:00:00 EST 1818

Sleeping for a While

You can sleep for any period of time from one millisecond up to the lifetime of your computer. For example, the following program would sleep for 3 seconds −

Example

import java.util.*;

public class SleepDemo {

  public static void main(String args[]) {

     try {

        System.out.println(new Date( ) + "\n");

        Thread.sleep(5*60*10);

        System.out.println(new Date( ) + "\n");

     }catch (Exception e) {

        System.out.println("Got an exception!");

     }

  }

}

This will produce the following result −

Output

Sun May 03 18:04:41 GMT 2009

Sun May 03 18:04:51 GMT 2009

Measuring Elapsed Time

Sometimes, you may need to measure point in time in milliseconds. So let's re-write the above example once again −

Example

import java.util.*;

public class DiffDemo {

  public static void main(String args[]) {

     try {

        long start = System.currentTimeMillis( );

        System.out.println(new Date( ) + "\n");

        Thread.sleep(5*60*10);

        System.out.println(new Date( ) + "\n");

        long end = System.currentTimeMillis( );

       long diff = end - start;

        System.out.println("Difference is : " + diff);

     }catch (Exception e) {

        System.out.println("Got an exception!");

     }

  }

}

This will produce the following result −

Output

Sun May 03 18:16:51 GMT 2009

Sun May 03 18:16:57 GMT 2009

Difference is : 5993

GregorianCalendar Class

GregorianCalendar is a concrete implementation of a Calendar class that implements the normal Gregorian calendar with which you are familiar. We did not discuss Calendar class in this tutorial, you can look up standard Java documentation for this.

The getInstance( ) method of Calendar returns a GregorianCalendar initialized with the current date and time in the default locale and time zone. GregorianCalendar defines two fields: AD and BC. These represent the two eras defined by the Gregorian calendar.

There are also several constructors for GregorianCalendar objects −

Here is the list of few useful support methods provided by GregorianCalendar class −

Example

import java.util.*;

public class GregorianCalendarDemo {

  public static void main(String args[]) {

     String months[] = {"Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep",

        "Oct", "Nov", "Dec"};

     int year;

     // Create a Gregorian calendar initialized

     // with the current date and time in the

     // default locale and timezone.

     GregorianCalendar gcalendar = new GregorianCalendar();

     // Display current time and date information.

     System.out.print("Date: ");

     System.out.print(months[gcalendar.get(Calendar.MONTH)]);

    System.out.print(" " + gcalendar.get(Calendar.DATE) + " ");

     System.out.println(year = gcalendar.get(Calendar.YEAR));

     System.out.print("Time: ");

     System.out.print(gcalendar.get(Calendar.HOUR) + ":");

     System.out.print(gcalendar.get(Calendar.MINUTE) + ":");

     System.out.println(gcalendar.get(Calendar.SECOND));

     // Test if the current year is a leap year

     if(gcalendar.isLeapYear(year)) {

        System.out.println("The current year is a leap year");

     }else {

       System.out.println("The current year is not a leap year");

     }

  }

}

This will produce the following result −

Output

Date: Apr 22 2009

Time: 11:25:27

The current year is not a leap year

For a complete list of constant available in Calendar class, you can refer the standard Java documentation.