java 获取指定小时前后

public static void main(String[] args) {
        Calendar calendar = Calendar.getInstance();
         calendar.set(Calendar.HOUR_OF_DAY, calendar.get(Calendar.HOUR_OF_DAY) - 10);
        SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        System.out.println("一个小时前：" + df.format(calendar.getTime()));
        System.out.println("当前的时间：" + df.format(new Date()));

    }