java求n小时候的时间

Calendar c = Calendar.getInstance();
    		Date date = new Date();
    		c.setTime(date);
//    		c.add(Calendar.DAY_OF_MONTH, -2);
    		c.add(Calendar.HOUR_OF_DAY, -48);
    		SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    		String searchDate = sdf.format(c.getTime());
System.out.println(searchDate);