From cc2ca4ac2927a762b8b08c0015c9c5cd1c3c21d3 Mon Sep 17 00:00:00 2001 From: gaoshihang <472024406@qq.com> Date: Mon, 25 Jul 2016 15:05:02 +0800 Subject: [PATCH 1/2] Create why-is-subtracting-these-two-times-in-1927-giving-a-strange-result.md MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 这是我翻译的why-is-subtracting-these-two-times-in-1927-giving-a-strange-result这篇问答的中文版。 --- ...o-times-in-1927-giving-a-strange-result.md | 59 +++++++++++++++++++ 1 file changed, 59 insertions(+) create mode 100644 contents/why-is-subtracting-these-two-times-in-1927-giving-a-strange-result.md diff --git a/contents/why-is-subtracting-these-two-times-in-1927-giving-a-strange-result.md b/contents/why-is-subtracting-these-two-times-in-1927-giving-a-strange-result.md new file mode 100644 index 0000000..d2f4449 --- /dev/null +++ b/contents/why-is-subtracting-these-two-times-in-1927-giving-a-strange-result.md @@ -0,0 +1,59 @@ +##为什么这两个时间（1927年）相减会得到一个奇怪的结果？ + +###问题描述 +如果我运行如下的程序，将两个相距一秒的日期解析成字符串并比较他们。 +``` +public static void main(String[] args) throws ParseException { + SimpleDateFormat sf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); + String str3 = "1927-12-31 23:54:07"; + String str4 = "1927-12-31 23:54:08"; + Date sDt3 = sf.parse(str3); + Date sDt4 = sf.parse(str4); + long ld3 = sDt3.getTime() /1000; + long ld4 = sDt4.getTime() /1000; + System.out.println(ld4-ld3); +} +``` + +输出结果为: +``` +353 +``` + +为什么`ld4-ld3`不是`1`（正如我所期望的那样），而是`353`? + +如果我把时间改变为之后的一秒: +``` +String str3 = "1927-12-31 23:54:08"; +String str4 = "1927-12-31 23:54:09"; +``` + +这时，`ld4-ld3`的结果为`1`. + +java版本： +``` +java version "1.6.0_22" +Java(TM) SE Runtime Environment (build 1.6.0_22-b04) +Dynamic Code Evolution Client VM (build 0.2-b02-internal, 19.0-b04-internal, mixed mode) +``` + +时区： +``` +sun.util.calendar.ZoneInfo[id="Asia/Shanghai", +offset=28800000,dstSavings=0, +useDaylight=false, +transitions=19, +lastRule=null] + +Locale(Locale.getDefault()): zh_CN +``` + +###问题回答 +这是因为1927年11月31日上海的时区改变了。 +观看[此页](http://www.timeanddate.com/time/change/china/shanghai?year=1927)获得更多关于上海1927年的细节。 +这个问题主要是由于在1927年12月31日的午夜，时钟回调了5分钟零52秒。 +所以"1927-12-31 23:54:08"这个时间实际上发生了两次，看上去java将这个时间解析为之后的那个瞬间。 +因此出现了这种差别。 + +这只是美好但奇怪的世界时区中的一个插曲。 + From bbe5225c9b0cb85f2705bd560e48587e54f312ad Mon Sep 17 00:00:00 2001 From: gaoshihang <472024406@qq.com> Date: Mon, 25 Jul 2016 15:16:25 +0800 Subject: [PATCH 2/2] Update why-is-subtracting-these-two-times-in-1927-giving-a-strange-result.md --- ...ubtracting-these-two-times-in-1927-giving-a-strange-result.md | 1 + 1 file changed, 1 insertion(+) diff --git a/contents/why-is-subtracting-these-two-times-in-1927-giving-a-strange-result.md b/contents/why-is-subtracting-these-two-times-in-1927-giving-a-strange-result.md index d2f4449..d436087 100644 --- a/contents/why-is-subtracting-these-two-times-in-1927-giving-a-strange-result.md +++ b/contents/why-is-subtracting-these-two-times-in-1927-giving-a-strange-result.md @@ -57,3 +57,4 @@ Locale(Locale.getDefault()): zh_CN 这只是美好但奇怪的世界时区中的一个插曲。 +stackoverflow链接：[Why is subtracting these two times (in 1927) giving a strange result?](http://stackoverflow.com/questions/6841333/why-is-subtracting-these-two-times-in-1927-giving-a-strange-result)