Java 为什么使用 SimpleDateFormat("hh:mm aa") 解析“23:00 PM”会返回上午 11 点？
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Why does parsing '23:00 PM' with SimpleDateFormat("hh:mm aa") return 11 a.m.?
提问by OscarRyz
Why does parsing '23:00 PM' with SimpleDateFormat("hh:mm aa")return 11 a.m.?
为什么在SimpleDateFormat("hh:mm aa")上午 11 点解析“23:00 PM” ？
采纳答案by Hyman Leow
You should be getting an exception, since "23:00 PM" is not a valid string, but Java's date/time facility is lenientby default, when handling date parsing.
你应该得到一个异常，因为“23:00 PM”不是一个有效的字符串，但在处理日期解析时，Java 的日期/时间工具默认是宽松的。
The logic is that 23:00 PM is 12 hours after 11:00 PM, which is 11:00 AM the following day. You'll also see things like "April 31" being parsed as "May 1" (one day after April 30).
逻辑是 23:00 PM 是 11:00 PM 之后的 12 小时，也就是第二天的上午 11:00。您还会看到诸如“4 月 31 日”之类的内容被解析为“5 月 1 日”（4 月 30 日之后的一天）。
If you don't want this behavior, set the lenient property to false on your SimpleDateFormat using DateFormat#setLenient(boolean), and you'll get an exception when passing in invalid date/times.
如果您不希望出现这种行为，请使用DateFormat#setLenient(boolean)在 SimpleDateFormat上将 lenient属性设置为 false ，并且在传入无效日期/时间时会出现异常。
回答by Evan Teran
I would guess that it does something like:
我猜它会做类似的事情：
hours = hours % 12;
to ensure that the hours are in the proper range.
以确保时间在适当的范围内。
回答by Steve McLeod
You want "HH:mm aa" as your format, if you will be parsing 24-hour time.
如果您要解析 24 小时制，您需要“HH:mm aa”作为您的格式。
public static void main(String[] args) throws ParseException {
SimpleDateFormat df = new SimpleDateFormat("HH:mm aa");
final Date date = df.parse("23:00 PM");
System.out.println("date = " + df.format(date));
}
outputs
产出
date = 23:00 PM
回答by thelsdj
Have you tried HH:mm aa?
你试过HH:mm aa吗？
HHis for 24 hour while hhis for 12.
HH是 24 小时，而hh12小时。
回答by Greg
23:00 PM could be thought of as 11 AM the next day. Javascript and PHP work like this pretty much but I can't speak for Java.
23:00 PM 可以被认为是第二天上午 11 点。Javascript 和 PHP 的工作方式差不多，但我不能说 Java。
回答by Peter Recore
Here are the formatting options specifed in the javadoc
以下是javadoc 中指定的格式选项
H Hour in day (0-23)
k Hour in day (1-24)
K Hour in am/pm (0-11)
h Hour in am/pm (1-12)
Notice that "h" would be for hours 1-12. If you want to handle 1-24, try "k". for 0-23 try "H". But I would not expect valid results if you are putting in impossible data.
请注意，“h”将表示 1-12 小时。如果要处理 1-24，请尝试“k”。对于 0-23 尝试“H”。但是，如果您输入不可能的数据，我不会期望得到有效的结果。
