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;
    }