java 日期前後推算計算

public class DateTest {

    public static void main(String[] args) {
        Date date = new Date(); // 新建一個日期

        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd"); // 格式化日期

        String beforeDate = sdf.format(getDateBefore(date, 10));
        System.out.println(beforeDate);
        String afterDate = sdf.format(getDateAfter(date, 10));
        System.out.println(afterDate);
    }

    /**
     * 得到幾天前的時間
     */

    public static Date getDateBefore(Date d, int day) {
        Calendar now = Calendar.getInstance();
        now.setTime(d);
        now.set(Calendar.DATE, now.get(Calendar.DATE) - day);
        return now.getTime();
    }

    /**
     * 得到幾天後的時間
     */

    public static Date getDateAfter(Date d, int day) {
        Calendar now = Calendar.getInstance();
        now.setTime(d);
        now.set(Calendar.DATE, now.get(Calendar.DATE) + day);
        return now.getTime();
    }
}