java计算时间

/**
* 计算指定日期的下一天
*
* @param dateTime
*            日期，格式为：yyyy-MM-dd
* @return
*/
public static String getNextDay(String dateTime) {
   Calendar now = Calendar.getInstance();
   SimpleDateFormat simpledate = new SimpleDateFormat("yyyy-MM-dd");
   Date date = null;
  try {
    date = (dateTime);
   } catch (ParseException ex) {
    System.out.println("日期格式不符合要求：" + ());
   return null;
   }
   (date);
  int year = (Calendar.YEAR);
  int month = (Calendar.MONTH);
  int day = (Calendar.DAY_OF_MONTH) + 1;
   (year, month, day);
   String time = (());
  return time;
}

/**
* 得到指定月的天数
* @param _year
* @param _month
* @return
*/
public static int getMaxDayOfMonth(int _year, int _month){
   Calendar now = Calendar.getInstance();
  int year = 0;
  int month = 0;
  if(_month==1){
    year = _year - 1;
    month = 12;
   }else{
    year = _year;
    month = _month - 1;
   }
  
   (Calendar.YEAR, year);
   (Calendar.MONTH, month);