Java獲取多少天之前的日期

 //計算日期
 private  String getPastDate(int past) {
     Calendar calendar = Calendar.getInstance();
     calendar.set(Calendar.DAY_OF_YEAR, calendar.get(Calendar.DAY_OF_YEAR) - past);
     Date today = calendar.getTime();
     SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");
     String result = format.format(today);
     return result;
 }