DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

        //方法1(推荐，功能强大灵活多变)

        Calendar calendar = Calendar.getInstance();

        calendar.add(Calendar.HOUR_OF_DAY, 3);//加3小时，当我减3小时的时候，这里3修改为-3，就可

        System.out.println(dateFormat.format(Calendar.getInstance().getTime()));

        System.out.println(dateFormat.format(calendar.getTime()));

        //方法2

        Date date = new Date();

        date.setTime(date.getTime() + (3 * 60 * 60 * 1000));//加3小时

        System.out.println(dateFormat.format(new Date()));

        System.out.println(dateFormat.format(date));

        Date nowDate = new Date();

        try {

            //暂停2秒

            Thread.sleep(2000);

        } catch (InterruptedException e) {

            e.printStackTrace();

        }

        //可以这样初始化，记住Date的初始化可以带参数

        Date aDate = new Date(nowDate.getTime());

        //可以增加间隔,增加1000毫秒

        Date bDate = new Date(nowDate.getTime() + 1000);

        System.out.println(nowDate.getTime());

        System.out.println(aDate.getTime());

        System.out.println(bDate.getTime());

        DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

        //方法1(推荐，功能强大灵活多变)

        Calendar calendar = Calendar.getInstance();

        calendar.add(Calendar.YEAR, -1);//时间减掉一年.

        System.out.println(dateFormat.format(Calendar.getInstance().getTime()));

        System.out.println(dateFormat.format(calendar.getTime()));