Java - Date & Time

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

The Date class supports two constructors. The first constructor initializes the object with the current date and time.

Date( )

The following constructor accepts one argument that equals the number of milliseconds that have elapsed since midnight, January 1, 1970

Date(long millisec)

Once you have a Date object available, you can call any of the following support methods to play with dates:

SNMethods with Description
1boolean after(Date date)
Returns true if the invoking Date object contains a date that is later than the one specified by date, otherwise, it returns false.
2boolean before(Date date)
Returns true if the invoking Date object contains a date that is earlier than the one specified by date, otherwise, it returns false.
3Object clone( )
Duplicates the invoking Date object.
4int compareTo(Date date)
Compares the value of the invoking object with that of date. Returns 0 if the values are equal. Returns a negative value if the invoking object is earlier than date. Returns a positive value if the invoking object is later than date.
5int compareTo(Object obj)
Operates identically to compareTo(Date) if obj is of class Date. Otherwise, it throws a ClassCastException.
6boolean equals(Object date)
Returns true if the invoking Date object contains the same time and date as the one specified by date, otherwise, it returns false.
7long getTime( )
Returns the number of milliseconds that have elapsed since January 1, 1970.
8int hashCode( )
Returns a hash code for the invoking object.
9void setTime(long time)
Sets the time and date as specified by time, which represents an elapsed time in milliseconds from midnight, January 1, 1970
10String toString( )
Converts the invoking Date object into a string and returns the result.

Getting Current Date & Time

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

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 would produce the following result:

Mon May 04 09:51:52 CDT 2009

Date Comparison:

There are following 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. For 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 would produce the following result:

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:

CharacterDescriptionExample
GEra designatorAD
yYear in four digits2001
MMonth in yearJuly or 07
dDay in month10
hHour in A.M./P.M. (1~12)12
HHour in day (0~23)22
mMinute in hour30
sSecond in minute55
SMillisecond234
EDay in weekTuesday
DDay in year360
FDay of week in month2 (second Wed. in July)
wWeek in year40
WWeek in month1
aA.M./P.M. markerPM
kHour in day (1~24)24
KHour in A.M./P.M. (0~11)10
zTime zoneEastern Standard Time
'Escape for textDelimiter
"Single quote`

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

     System.out.printf(str);
  }
}

This would produce the following result:

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 $. For 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 would produce the following result:

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. For 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 would produce the following result:

Due date: February 09, 2004

Date and Time Conversion Characters:

CharacterDescriptionExample
cComplete date and timeMon May 04 09:51:52 CDT 2009
FISO 8601 date2004-02-09
DU.S. formatted date (month/day/year)02/09/2004
T24-hour time18:05:19
r12-hour time06:05:19 pm
R24-hour time, no seconds18:05
YFour-digit year (with leading zeroes)2004
yLast two digits of the year (with leading zeroes)04
CFirst two digits of the year (with leading zeroes)20
BFull month nameFebruary
bAbbreviated month nameFeb
mTwo-digit month (with leading zeroes)02
dTwo-digit day (with leading zeroes)03
eTwo-digit day (without leading zeroes)9
AFull weekday nameMonday
aAbbreviated weekday nameMon
jThree-digit day of year (with leading zeroes)069
HTwo-digit hour (with leading zeroes), between 00 and 2318
kTwo-digit hour (without leading zeroes), between 0 and 2318
ITwo-digit hour (with leading zeroes), between 01 and 1206
lTwo-digit hour (without leading zeroes), between 1 and 126
MTwo-digit minutes (with leading zeroes)05
STwo-digit seconds (with leading zeroes)19
LThree-digit milliseconds (with leading zeroes)047
NNine-digit nanoseconds (with leading zeroes)047000000
PUppercase morning or afternoon markerPM
pLowercase morning or afternoon markerpm
zRFC 822 numeric offset from GMT-0800
ZTime zonePST
sSeconds since 1970-01-01 00:00:00 GMT1078884319
QMilliseconds since 1970-01-01 00:00:00 GMT1078884319047

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. For 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:

$ java DateDemo
1818-11-11 Parses as Wed Nov 11 00:00:00 GMT 1818
$ java DateDemo 2007-12-01
2007-12-01 Parses as Sat Dec 01 00:00:00 GMT 2007

Sleeping for a While:

You can sleep for any period of time from one millisecond up to the lifetime of your computer. For example, following program would sleep for 10 seconds:

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 would produce the following result:

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 above example once again:

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 would produce the following result:

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. I did not discuss Calendar class in this tutorial, you can look 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:

SNConstructor with Description
1GregorianCalendar()
Constructs a default GregorianCalendar using the current time in the default time zone with the default locale.
2GregorianCalendar(int year, int month, int date)
Constructs a GregorianCalendar with the given date set in the default time zone with the default locale.
3GregorianCalendar(int year, int month, int date, int hour, int minute)
Constructs a GregorianCalendar with the given date and time set for the default time zone with the default locale.
4GregorianCalendar(int year, int month, int date, int hour, int minute, int second)
Constructs a GregorianCalendar with the given date and time set for the default time zone with the default locale.
5GregorianCalendar(Locale aLocale)
Constructs a GregorianCalendar based on the current time in the default time zone with the given locale.
6GregorianCalendar(TimeZone zone)
Constructs a GregorianCalendar based on the current time in the given time zone with the default locale.
7GregorianCalendar(TimeZone zone, Locale aLocale)
Constructs a GregorianCalendar based on the current time in the given time zone with the given locale.

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

SNMethods with Description
1void add(int field, int amount)
Adds the specified (signed) amount of time to the given time field, based on the calendar's rules.
2protected void computeFields()
Converts UTC as milliseconds to time field values.
3protected void computeTime()
Overrides Calendar Converts time field values to UTC as milliseconds.
4boolean equals(Object obj)
Compares this GregorianCalendar to an object reference.
5int get(int field)
Gets the value for a given time field.
6int getActualMaximum(int field)
Return the maximum value that this field could have, given the current date.
7int getActualMinimum(int field)
Return the minimum value that this field could have, given the current date.
8int getGreatestMinimum(int field)
Returns highest minimum value for the given field if varies.
9Date getGregorianChange()
Gets the Gregorian Calendar change date.
10int getLeastMaximum(int field)
Returns lowest maximum value for the given field if varies.
11int getMaximum(int field)
Returns maximum value for the given field.
12Date getTime()
Gets this Calendar's current time.
13long getTimeInMillis()
Gets this Calendar's current time as a long.
14TimeZone getTimeZone()
Gets the time zone.
15int getMinimum(int field)
Returns minimum value for the given field.
16int hashCode()
Override hashCode.
17boolean isLeapYear(int year)
Determines if the given year is a leap year.
18void roll(int field, boolean up)
Adds or subtracts (up/down) a single unit of time on the given time field without changing larger fields.
19void set(int field, int value)
Sets the time field with the given value.
20void set(int year, int month, int date)
Sets the values for the fields year, month, and date.
21void set(int year, int month, int date, int hour, int minute)
Sets the values for the fields year, month, date, hour, and minute.
22void set(int year, int month, int date, int hour, int minute, int second)
Sets the values for the fields year, month, date, hour, minute, and second.
23void setGregorianChange(Date date)
Sets the GregorianCalendar change date.
24void setTime(Date date)
Sets this Calendar's current time with the given Date.
25void setTimeInMillis(long millis)
Sets this Calendar's current time from the given long value.
26void setTimeZone(TimeZone value)
Sets the time zone with the given time zone value.
27String toString()
Return a string representation of this calendar.

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 would produce the following result:

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 to standard Java documentation.




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