Java 日期比较以及得到前后一天

/**
* 比较两个指定时间，结果为0 表示相同，< 0 则表示第一个时间早于第二个时间
* @param firstDay
* @param secondDay
* @return
*/
public static int compareto(String firstDay,String secondDay)
{
Calendar c = Calendar.getInstance();
Calendar c2 = Calendar.getInstance();
Date date = null;
Date date2 = null;
try
{
date = new SimpleDateFormat(DATE_FORMAT_PATTERN).parse(firstDay);
date2 = new SimpleDateFormat(DATE_FORMAT_PATTERN).parse(secondDay);
}
catch (ParseException e)
{
e.printStackTrace();
}
c.setTime(date);
c2.setTime(date2);
return c.compareTo(c2);
}

/**
* 获得指定日期的前n天
*
* @param specifiedDay yy-MM-dd
* @return
* @throws Exception
*/
public static String getBeforeDay(String specifiedDay,int n)
{
Calendar c = Calendar.getInstance();
Date date = null;
try
{
date = new SimpleDateFormat(DATE_FORMAT_PATTERN).parse(specifiedDay);
}
catch (ParseException e)
{
e.printStackTrace();
}
c.setTime(date);
int day = c.get(Calendar.DATE);
c.set(Calendar.DATE, day - n);

String dayBefore = new SimpleDateFormat(DATE_FORMAT_PATTERN).format(c.getTime());
return dayBefore;
}

/**
* 获得指定日期的后一天
*
* @param specifiedDay yy-MM-dd
* @return
*/
public static String getAfterDay(String specifiedDay,int n)
{
Calendar c = Calendar.getInstance();
Date date = null;
try
{
date = new SimpleDateFormat(DATE_FORMAT_PATTERN).parse(specifiedDay);
}
catch (ParseException e)
{
e.printStackTrace();
}
c.setTime(date);
int day = c.get(Calendar.DATE);
c.set(Calendar.DATE, day + n);

String dayAfter = new SimpleDateFormat(DATE_FORMAT_PATTERN).format(c.getTime());
return dayAfter;
}