日历的 getActualMinimum 返回错误值

Question

我需要将某个日期与当前日期/时间进行比较，以确保它在当月的第一天/小时/分钟/秒之前。为了实现此功能，使用其 getActualMinimum 方法配置 Calendar 实例，但是，今天（星期四，19/01/2023 - 10:40:18 BRT 2023），它呈现了我从未有过的行为面对过。考虑以下代码：

    Calendar cal = Calendar.getInstance();
    System.out.println("After instantiation:                  " + cal.getTime());
    
    cal.set(Calendar.DAY_OF_MONTH, cal.getActualMinimum(Calendar.DAY_OF_MONTH));
    System.out.println("After configuring the Day of Month:   " + cal.getTime());
    
    cal.set(Calendar.HOUR_OF_DAY, cal.getActualMinimum(Calendar.HOUR_OF_DAY));
    System.out.println("After configuring the Hour of day:    " + cal.getTime());
    
    cal.set(Calendar.MINUTE, cal.getActualMinimum(Calendar.MINUTE));
    System.out.println("After configuring the Minutes:        " + cal.getTime());
    
    cal.set(Calendar.SECOND, cal.getActualMinimum(Calendar.SECOND));
    System.out.println("After configuring the Seconds:        " + cal.getTime());
    
    cal.set(Calendar.MILLISECOND, cal.getActualMinimum(Calendar.MILLISECOND));
    System.out.println("After configuring the Millis:         " + cal.getTime());

上面的代码，在创建这篇文章的那一刻，将打印到控制台：

After instantiation:                  Thu Jan 19 10:40:18 BRT 2023
After configuring the Day of Month:   Sun Jan 01 10:40:18 BRT 2023
After configuring the Hour of day:    Sat Dec 31 23:40:18 BRT 2022
After configuring the Minutes:        Sat Dec 31 23:00:18 BRT 2022
After configuring the Seconds:        Sat Dec 31 23:00:00 BRT 2022
After configuring the Millis:         Sat Dec 31 23:00:00 BRT 2022

有人可以解释为什么在配置一天中的小时后，该值设置为23并不是00？

Answer 1

可能是你电脑的默认TimeZone导致的，在你声明Calnedar对象后尝试添加这个

cal.setTimeZone(TimeZone.getTimeZone("UTC"));