grc.add(GregorianCalendar.MONTH,2);
   System.out.println("grc="+dateFormat.format(grc.getTime()));  
  }
 }

日期加上天數(shù)的運(yùn)算：

import java.util.*;

.....
java.sql.Date d;
.....
Calendar c = Calendar.getInstance();
c.setTime(d);
c.add(Calendar.DATE, 3); // 加3天
java.util.Date t = c.getTime();
d = new java.sql.Date(t.getTime());

 

7、計(jì)算日期之間的間隔
<%@ page import="java.util.Date"%>
<%@ page import="java.text.DateFormat"%>
<%
String input = "2003-05-01";
SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd");
Date d1 = null;
try{
d1 = formatter.parse(input);
}catch(ParseException e){
out.println("unparseable using " + formatter);
}

Date d2 = new Date();

long diff = d2.getTime() - d1.getTime();
out.println("Difference is " + (diff/(1000*60*60*24)) + " days.");
%>
輸出結(jié)果為：
Difference is 29 days.

8,、日期的加減運(yùn)算
方法：用Calendar類的add()方法
<%@ page import="java.util.*"%>
<%@ page import="java.text.*"%>
<%
Calendar now = Calendar.getInstance();
SimpleDateFormat formatter = new SimpleDateFormat("E yyyy.MM.dd ‘a(chǎn)t‘ hh:mm:ss a zzz");
out.println("It is now " + formatter.format(now.getTime()));
now.add(Calendar.DAY_OF_YEAR,-(365*2));
out.println("<br>");
out.println("Two years ago was " + formatter.format(now.getTime()));
%>
輸出結(jié)果為：
It is now 星期五 2003.05.30 at 01:45:32 下午 CST
Two years ago was 星期三 2001.05.30 at 01:45:32 下午 CST

9、比較日期
方法：用equals(),、before(),、after()方法
<%@ page import="java.util.*"%>
<%@ page import="java.text.*"%>
<%
DateFormat df = new SimpleDateFormat("yyy-MM-dd");
Date d1 = df.parse("2000-01-01");
Date d2 = df.parse("1999-12-31");

String relation = null;
if(d1.equals(d2))
relation = "the same date as";
else if(d1.before(d2))
relation = "before";
else
relation = "after";
out.println(d1 +" is " + relation + ‘ ‘ + d2);
%>
輸出結(jié)果為：
Sat Jan 01 00:00:00 CST 2000 is after Fri Dec 31 00:00:00 CST 1999

10、記錄一件事所花費(fèi)的時(shí)間
方法：調(diào)用兩次System.getTimeMillis()方法,，求差值
<%@ page import="java.text.*"%>
<%
long t0,t1;
t0 = System.currentTimeMillis();
out.println("Cyc starts at " + t0);
int k = 0;
for(int i =0;i<100000;i++){
k += i;
}
t1 = System.currentTimeMillis();
out.println("<br>");
out.println("Cyc ends at " + t1);
out.println("<br>");
out.println("This run took " + (t1-t0) + "ms.");
%>

輸出結(jié)果為：
Cyc starts at 1054275312432
Cyc ends at 1054275312442
This run took 10ms.

其它：如何格式化小數(shù)

<%@ page import="java.text.*"%>
<%
DecimalFormat df = new DecimalFormat(",###.00");
double aNumber = 33665448856.6568975;
String result = df.format(aNumber);
out.println(result);
%>

輸出結(jié)果為：
33,665,448,856.66