获取N天前的日期和N天后的日期

一个比较好的工具方法，获取N天的日期和N天后的日期，拿来借鉴学习

/**
    * 获取过去第几天的日期
    *
    * @param past
    * @return
    */
   public static 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);
       Log.e(null, result);
       return result;
   }

   /**
    * 获取未来 第 past 天的日期
    * @param past
    * @return
    */
   public static String getFetureDate(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);
       Log.e(null, result);
       return result;
   }