java獲得指定時間幾天前或幾天后的日期

/**
   * 得到幾天前的時間
   * @param d
   * @param day
   * @return
   */
  public static Date getDateBefore(Date d,int day){
   Calendar now =Calendar.getInstance();
   now.setTime(d);
   now.set(Calendar.DATE,now.get(Calendar.DATE)-day);
   return now.getTime();
  }

  /**
   * 得到幾天后的時間
   * @param d
   * @param day
   * @return
   */
  public static Date getDateAfter(Date d,int day){
   Calendar now =Calendar.getInstance();
   now.setTime(d);
   now.set(Calendar.DATE,now.get(Calendar.DATE)+day);
   return now.getTime();
  }