Java Time/ Date / Calendar example

// 간단한 현재 날짜/시간 얻기

import java.util.Date;

  

public class DateDemo {

   public static void main(String args[]) {

       

   Date date = new Date();  

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

   }

}

Mon May 04 09:51:52 CDT 2009

// 날짜/시간  데이터 포맷팅 

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));

   }

}

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

// Printf 를 이용한 데이터 포맷팅 !

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);

  }

}

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

//Calendar 를 통한  시간 비교 ( 현재 시간이  과거에 기록된 시간에  비해 몇초 지났나? ) 

public boolean isAdjustedTarget(int reforceTimeSec){

if(isAdjusted == false)  // 수요조절된적이 없으면 조절대상이 됨. 

return true;

Calendar currentDate = Calendar.getInstance();

System.out.println(currentDate.get(Calendar.YEAR));

System.out.println(currentDate.get(Calendar.MONTH) + 1);

System.out.println(currentDate.get(Calendar.DATE));

System.out.println(currentDate.get(Calendar.HOUR));

System.out.println(currentDate.get(Calendar.MINUTE));

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

if((currentDate.getTimeInMillis() - endAdjustedTime.getTimeInMillis())  < (reforceTimeSec * 1000))

return false;

return true;

}

Simple DateFormat format codes:

Character	Description	Example
G	Era designator	AD
y	Year in four digits	2001
M	Month in year	July or 07
d	Day in month	10
h	Hour in A.M./P.M. (1~12)	12
H	Hour in day (0~23)	22
m	Minute in hour	30
s	Second in minute	55
S	Millisecond	234
E	Day in week	Tuesday
D	Day in year	360
F	Day of week in month	2 (second Wed. in July)
w	Week in year	40
W	Week in month	1
a	A.M./P.M. marker	PM
k	Hour in day (1~24)	24
K	Hour in A.M./P.M. (0~11)	10
z	Time zone	Eastern Standard Time
'	Escape for text	Delimiter
"	Single quote	`

Date and Time Conversion Characters:

Character	Description	Example
c	Complete date and time	Mon May 04 09:51:52 CDT 2009
F	ISO 8601 date	2004-02-09
D	U.S. formatted date (month/day/year)	02/09/2004
T	24-hour time	18:05:19
r	12-hour time	06:05:19 pm
R	24-hour time, no seconds	18:05
Y	Four-digit year (with leading zeroes)	2004
y	Last two digits of the year (with leading zeroes)	04
C	First two digits of the year (with leading zeroes)	20
B	Full month name	February
b	Abbreviated month name	Feb
m	Two-digit month (with leading zeroes)	02
d	Two-digit day (with leading zeroes)	03
e	Two-digit day (without leading zeroes)	9
A	Full weekday name	Monday
a	Abbreviated weekday name	Mon
j	Three-digit day of year (with leading zeroes)	069
H	Two-digit hour (with leading zeroes), between 00 and 23	18
k	Two-digit hour (without leading zeroes), between 0 and 23	18
I	Two-digit hour (with leading zeroes), between 01 and 12	06
l	Two-digit hour (without leading zeroes), between 1 and 12	6
M	Two-digit minutes (with leading zeroes)	05
S	Two-digit seconds (with leading zeroes)	19
L	Three-digit milliseconds (with leading zeroes)	047
N	Nine-digit nanoseconds (with leading zeroes)	047000000
P	Uppercase morning or afternoon marker	PM
p	Lowercase morning or afternoon marker	pm
z	RFC 822 numeric offset from GMT	-0800
Z	Time zone	PST
s	Seconds since 1970-01-01 00:00:00 GMT	1078884319
Q	Milliseconds since 1970-01-01 00:00:00 GMT	1078884319047

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