为什么减去这两次(1927年)得到一个奇怪的结果呢？

If I run the following program, which parses two date strings referencing times 1 second apart and compares them:

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);
}

The output is:

353

Why is ld4-ld3 not 1 (as I would expect from the one-second difference in the times), but 353?

If I change the dates to times 1 second later:

String str3 = "1927-12-31 23:54:08";  
String str4 = "1927-12-31 23:54:09";  

Then ld4-ld3 will be 1.

Java version:

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)

Timezone(`TimeZone.getDefault()`):

sun.util.calendar.ZoneInfo[id="Asia/Shanghai",
offset=28800000,dstSavings=0,
useDaylight=false,
transitions=19,
lastRule=null]

Locale(Locale.getDefault()): zh_CN

The moral of this strangeness is:

• Use dates and times in UTC wherever possible.
• If you can not display a date or time in UTC, always indicate the time-zone.
• If you can not require an input date/time in UTC, require an explicitly indicated time-zone.

When incrementing time you should convert back to UTC and then add or subtract. Use the local time only for display.

This way you will be able to walk through any periods where hours or minutes happen twice.

If you converted to UTC, add each second, and convert to local time for display. You would go through 11:54:08 p.m. LMT - 11:59:59 p.m. LMT and then 11:54:08 p.m. CST - 11:59:59 p.m. CST.

Instead of converting each date, you use the following code

long difference = (sDt4.getTime() - sDt3.getTime()) / 1000;
System.out.println(difference);

And see the result is:

1

I'm sorry to say that, but the time discontinuity has moved a bit in

JDK 6 two years ago, and in JDK 7 just recently in update 25.

Lesson to learn: avoid non-UTC times at all costs, except, maybe, for display.

IMHO the pervasive, implicit localization in Java is its single largest design flaw. It may be intended for user interfaces, but frankly, who really uses Java for user interfaces today except for some IDEs where you can basically ignore localization because programmers aren't exactly the target audience for it. You can fix it (especially on Linux servers) by:

• export LC_ALL=C TZ=UTC
• set your system clock to UTC
• never use localized implementations unless absolutely necessary (ie for display only)

To the Java Community Process members I recommend:

• make localized methods not the default, but require the user to explicitly request localization.
• use UTF-8/UTC as the FIXED default instead because that's simply the default today. There is no reason to do something else, except if you want to produce threads like this.

I mean, come on, aren't global static variables an anti-OO pattern? Nothing else is those pervasive defaults given by some rudimentary environment variables.......