比如：现在是2004-03-26 13：31：40
      过去是：2004-01-02 11：30：24
我现在要获得两个日期差，差的形式为：XX天XX小时XX分XX秒

方法一：
DateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

try
{
   Date d1 = df.parse("2004-03-26 13:31:40");
   Date d2 = df.parse("2004-01-02 11:30:24");
   long diff = d1.getTime() - d2.getTime();
   long days = diff / (1000 * 60 * 60 * 24);
}
catch (Exception e)
{
}

方法二：   SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
  java.util.Date now = df.parse("2004-03-26 13:31:40");
  java.util.Date date=df.parse("2004-01-02 11:30:24");
  long l=now.getTime()-date.getTime();
  long day=l/(24*60*60*1000);
  long hour=(l/(60*60*1000)-day*24);
  long min=((l/(60*1000))-day*24*60-hour*60);
  long s=(l/1000-day*24*60*60-hour*60*60-min*60);
  System.out.println(""+day+"天"+hour+"小时"+min+"分"+s+"秒");

方法三：
  SimpleDateFormat dfs = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
  java.util.Date begin=dfs.parse("2004-01-02 11:30:24");
  java.util.Date end = dfs.parse("2004-03-26 13:31:40");
  long between=(end.getTime()-begin.getTime())/1000;//除以1000是为了转换成秒

long day1=between/(24*3600);
  long hour1=between%(24*3600)/3600;
  long minute1=between%3600/60;
  long second1=between%60/60;
  System.out.println(""+day1+"天"+hour1+"小时"+minute1+"分"+second1+"秒");

====================================================

java 比较时间大小

String s1="2008-01-25 09:12:09";
String s2="2008-01-29 09:12:11";
java.text.DateFormat df=new java.text.SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
java.util.Calendar c1=java.util.Calendar.getInstance();
java.util.Calendar c2=java.util.Calendar.getInstance();
try
{
c1.setTime(df.parse(s1));
c2.setTime(df.parse(s2));
}catch(java.text.ParseException e){
System.err.println("格式不正确");
}
int result=c1.compareTo(c2);
if(result==0)
System.out.println("c1相等c2");
else if(result<0)
System.out.println("c1小于c2");
else
System.out.println("c1大于c2");