JDK 9 doc-api-only RFR of 6791812: (file spec) Incompatible File.lastModified() and setLastModified() for negative time

Brian Burkhalter brian.burkhalter at oracle.com
Mon May 22 22:55:58 UTC 2017

On May 22, 2017, at 3:52 PM, Stuart Marks <stuart.marks at oracle.com> wrote:

>> --- a/src/java.base/share/classes/java/io/File.java
>> +++ b/src/java.base/share/classes/java/io/File.java
>> @@ -932,7 +932,9 @@
>>      * @return  A <code>long</code> value representing the time the file was
>>      *          last modified, measured in milliseconds since the epoch
>>      *          (00:00:00 GMT, January 1, 1970), or <code>0L</code> if the
>> -     *          file does not exist or if an I/O error occurs
>> +     *          file does not exist or if an I/O error occurs; the value may
>> +     *          be negative in which case its absolute value indicates the
>> +     *          number of milliseconds before the epoch
>>      *
>>      * @throws  SecurityException
>>      *          If a security manager exists and its {@link
> This is "absolutely" pedantic, but the absolute value of Long.MIN_VALUE is Long.MIN_VALUE, which is still negative.


> A negative value for "milliseconds before the epoch" is confusing. It might be sufficient simply to say that negative values indicate a time prior to the epoch.

Or it could say “its mathematically absolute value” which would be accurate.

> This is not outside the realm of possibility. For example, the Mac HFS+ file system represents time as seconds since January 1, 1904. It seems unlikely :-) that any Mac files were actually created between 1904 and 1970, but it is a possibility that somebody could have set a file's timestamp to a date in that range.

Yes, I read about HFS Plus as part of investigating another time issue.

>> The weird thing here is that if this method were invoked on a file last
>> modified at 00:00:00 GMT, January 1, 1970, then we would not know whether the
>> file does not exist or whether its last-modified time is the epoch. It seems
>> to me that if the file does not exist it would be better to throw a
>> FileNotFoundException but that is not an issue for JDK 9 at this stage of
>> game.
> I'll comment on this on the subsequent thread.




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