java生成指定范围的随机日期

public static String randomDateBetweenMinAndMax(){     Calendar calendar = Calendar.getInstance();     //注意月份要减去1     calendar.set(1990,11,31);     calendar.getTime().getTime();     //根据需求，这里要将时分秒设置为0     calendar.set(Calendar.HOUR_OF_DAY, 0);     calendar.set(Calendar.MINUTE, 0);     calendar.set(Calendar.SECOND,0);     long min = calendar.getTime().getTime();;     calendar.set(2013,11,31);     calendar.set(Calendar.HOUR_OF_DAY,0);     calendar.set(Calendar.MINUTE,0);     calendar.set(Calendar.SECOND,0);     calendar.getTime().getTime();     long max = calendar.getTime().getTime();     //得到大于等于min小于max的double值     double randomDate = Math.random()*(max-min)+min;     //将double值舍入为整数，转化成long类型     calendar.setTimeInMillis(Math.round(randomDate));     return calendar.getTime().toString();   }