java关于日期

//毫秒转换为日期

public static void main(String[] args) {
      DateFormat formatter = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");

      long now = System.currentTimeMillis();

      Calendar calendar = Calendar.getInstance();
      calendar.setTimeInMillis(now);

      System.out.println(now + " = " + formatter.format(calendar.getTime()));

  // 日期转换为毫秒 两个日期想减得到天数

SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
     String start="2011-09-20 12:30:45";
     String end ="2011-10-20 6:30:00";
     //得到毫秒数
long timeStart=sdf.parse(start).getTime();
     long timeEnd =sdf.parse(end).getTime();
     //两个日期想减得到天数
long dayCount= (timeEnd-timeStart)/(24*3600*1000);
     System.out.println(dayCount);

  }

//获得指定天数后的日期

int timeinterval = 3;

Calendar ca = Calendar.getInstance();

ca.add(ca.DATE, timeinterval);
SimpleDateFormat bartDateFormat = new SimpleDateFormat("yyyy-MM-dd");
String latertime = bartDateFormat.format(ca.getTime());