创建对象

默认创建的对象的时间是当前时间

Calendar instance = Calendar.getInstance();

常用方法

get、set、add
set方法设置时间
get方法获取时间
add对当前时间进行加减操作

 Calendar instance = Calendar.getInstance();
        //Wed Jul 06 10:12:41 CST 2022
        System.out.println(instance.getTime());
        instance.set(Calendar.YEAR,1998);
        //后面参数0-11对应 1-12 12个月份
        instance.set(Calendar.MONTH,7);
        instance.set(Calendar.DATE,23);

        instance.set(Calendar.HOUR_OF_DAY, 22);
        instance.set(Calendar.MINUTE, 0);
        instance.set(Calendar.SECOND, 0);
        instance.set(Calendar.MILLISECOND, 0);
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        //1998-08-23 22:00:00
        System.out.println(simpleDateFormat.format(instance.getTime()));
        instance.add(Calendar.DAY_OF_YEAR, -2);
        //1998-08-21 22:00:00
        System.out.println(simpleDateFormat.format(instance.getTime()));