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import java.text.DecimalFormat
double a = 2.3659874;
//СÊý¸ñʽ»¯£¬ÒýºÅÖеÄ0.000±íʾ±£ÁôСÊýµãºóÈý루µÚËÄλËÄÉáÎåÈ룩
DecimalFormat df = new DecimalFormat("0.000");
String num = df.format(a);
System.out.println(num);
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±ÈÈ磺ÏÖÔÚÊÇ2004-03-26 13£º31£º40
       ¹ýÈ¥ÊÇ£º2004-01-02 11£º30£º24
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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)
{
}
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   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+"Ìì"+hour+"Сʱ"+min+"·Ö"+s+"Ãë");
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   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;//³ýÒÔ1000ÊÇΪÁËת»»³ÉÃë
   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+"Ìì"+hour1+"Сʱ"+minute1+"·Ö"+second1+"Ãë");
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