Java 指定日期和日期间隔，返回间隔 之前 | 之后 的日期

/** * Created by gongzi on 2016/9/9. */public class DateUtil {    /**     * 指定日期和日期间隔，返回间隔之前的日期     * @param specifiedDay     * @param interval     * @return     */    public static String getSpecifiedDayAgo(String specifiedDay, int interval){        return getSpecifiedDay(specifiedDay, interval, "-");    }    /**     * 指定日期和日期间隔，返回间隔之前的日期     * @param specifiedDay     * @param interval     * @return     */    public static String getSpecifiedDayAfter(String specifiedDay, int interval){        return getSpecifiedDay(specifiedDay, interval, "+");    }    private static String getSpecifiedDay(String specifiedDay, int interval, String func) {        Calendar c = Calendar.getInstance();        Date date = null;        try {            date = new SimpleDateFormat("yyyy-MM-dd").parse(specifiedDay);        } catch (ParseException e) {            e.printStackTrace();        }        c.setTime(date);        int day=c.get(Calendar.DATE);        if("+".equals(func)) {            c.set(Calendar.DATE, day + interval);        } else if("-".equals(func)) {            c.set(Calendar.DATE, day - interval);        } else {            return null;        }        String dayAfter = new SimpleDateFormat("yyyy-MM-dd").format(c.getTime());        return dayAfter;    }    public static void main(String[] args){        String d1 = getSpecifiedDayAfter("2017-01-11", 7);        String d2 = getSpecifiedDayAgo("2017-01-11", 7);        System.out.println(d1);        System.out.println(d2);    }}2017-01-182017-01-04