Date is often used in application logic.Many times we need display the date in the form of string which is user customed.For example,suppose we know a date whose year is 1990 and month is 3 and date is 25.Perhaps you hope to display the date in the form of Mar 25th 1990.Perhaps you also hope to display the date in the form of 1990 Mar 25.Perhaps in the form of 3-25-1990.

All of above may be called date format.So how can we format a date in the customed form? To resove this propblem,we refer to SimpleDateFormat class in J2SE of Java language of Sun.

In the below,we quote the documentation of SimpleDateFormat class of J2SE of Sun.

Date and time formats are specified by date and time pattern strings. Within date and time pattern strings, unquoted letters from 'A' to 'Z' and from 'a' to 'z' are interpreted as pattern letters representing the components of a date or time string. Text can be quoted using single quotes (') to avoid interpretation. "''" represents a single quote. All other characters are not interpreted; they're simply copied into the output string during formatting or matched against the input string during parsing. The following pattern letters are defined (all other characters from 'A' to 'Z' and from 'a' to 'z' are reserved):

Letter	Date or Time Component	Presentation	Examples
G	Era designator	Text	AD
y	Year	Year	1996; 96
M	Month in year	Month	July; Jul; 07
w	Week in year	Number	27
W	Week in month	Number	2
D	Day in year	Number	189
d	Day in month	Number	10
F	Day of week in month	Number	2
E	Day in week	Text	Tuesday; Tue
a	Am/pm marker	Text	PM
H	Hour in day (0-23)	Number	0
k	Hour in day (1-24)	Number	24
K	Hour in am/pm (0-11)	Number	0
h	Hour in am/pm (1-12)	Number	12
m	Minute in hour	Number	30
s	Second in minute	Number	55
S	Millisecond	Number	978
z	Time zone	General time zone	Pacific Standard Time; PST; GMT-08:00
Z	Time zone	RFC 822 time zone	-0800

The following examples show how date and time patterns are interpreted in the U.S. locale. The given date and time are 2001-07-04 12:08:56 local time in the U.S. Pacific Time time zone.

Date and Time Pattern	Result
"yyyy.MM.dd G 'at' HH:mm:ss z"	2001.07.04 AD at 12:08:56 PDT
"EEE, MMM d, ''yy"	Wed, Jul 4, '01
"h:mm a"	12:08 PM
"hh 'o''clock' a, zzzz"	12 o'clock PM, Pacific Daylight Time
"K:mm a, z"	0:08 PM, PDT
"yyyyy.MMMMM.dd GGG hh:mm aaa"	02001.July.04 AD 12:08 PM
"EEE, d MMM yyyy HH:mm:ss Z"	Wed, 4 Jul 2001 12:08:56 -0700
"yyMMddHHmmssZ"	010704120856-0700

The usage of patterns in JsJava is similar to that in Java.e.g as follows:

<script src="jsjava-2.0.js"></script> <script> var df=new SimpleDateFormat(); df.applyPattern("yyyy-MM-dd hh:mm:ss"); var date=new Date(2007,3,30,10,59,51); var str=df.format(date); document.write(str); </script> The display is : 2007-04-30 10:59:51

Use more,understand more!