java中计算时间差

Calendar cale = null;
        SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        Date d = new Date();
      //获取当前时间
        String startDate =format.format(d); 

       // 获取前月的第一天  

cale = Calendar.getInstance();

cale.add(Calendar.MONTH, 0);

cale.set(Calendar.DAY_OF_MONTH, 1);

firstday = format.format(cale.getTime());

// 获取前月的最后一天
        cale = Calendar.getInstance();
        cale.add(Calendar.MONTH, );
        cale.set(Calendar.DAY_OF_MONTH, );
        cale.set(Calendar.HOUR_OF_DAY,);
        cale.set(Calendar.MINUTE,);
        cale.set(Calendar.SECOND,);
        String endDate = format.format(cale.getTime()); 

　　获取当前时间的前一天或者前几天时间

　　  Date date=new Date();

　　  Calendar calendar = Calendar.getInstance();

calendar.setTime(date);

calendar.add(Calendar.DAY_OF_MONTH, -1);

date = calendar.getTime();

计算时间差

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

try

{

    Date d1 = df.parse("2008-03-26 13:31:40");

    Date d2 = df.parse("2008-01-02 11:30:24");

    long diff = d1.getTime() - d2.getTime();

    long days = diff / ( *  *  * );

}

catch (Exception e)

{

}