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From: Eric Sosman on 4 Nov 2009 10:01
Wojtek wrote:
> Eric Sosman wrote :
>> Wojtek wrote:
>>> Lew wrote :
>>>> Lew wrote :
>>>>>>> Map <TimeZone, String> map =
>>>>>>> new TreeMap <TimeZone, String> ( new Comparator <TimeZone> ()
>>>>>>> { .... } );
>>>>>
>>>>
>>>> Wojtek wrote:
>>>>>> No arguments that this does work.
>>>>>
>>>>>> However I was replying to your statement "'TimeZone' can easily be
>>>>>> a map
>>>>>> key, yes, even for a 'TreeMap'. " which appears to say that you do
>>>>>> not
>>>>>> need a custom Comparator:
>>>>>
>>>>
>>>> Even though I had explicitly mentioned a custom Comparator in the post
>>>> to which you were replying? Come on, now. Your explanation is
>>>> disingenuous at best.
>>>
>>> To me a 'key' is the part which goes into the 'K' part of Map<K,V>.
>>
>> Yes, that's right.
>>
>>> For a Comparator, the signature is Comparator<T> where the 'T' refers
>>> to a 'Type':
>>> http://www.j2ee.me/javase/6/docs/api/java/util/Comparator.html
>>
>> ... which means only that the K in Map<K,V> is the same as
>> the T in Comparator<T>, or is a subclass/subinterface of T. You
>> shouldn't read too much into the particular letters chosen to name
>> type parameters; the names are as arbitrary as those of method
>> parameters, and carry no deeper meaning.
>>
>> Does Map<String,String> bother you, because String == String
>> but K != V? If not, K != T shouldn't bother you, either, even if
>> you have a Map<Book,Date> and a Comparator<Book> with Book == Book.
>
> Semantics!
>
> We work in a precise field. An extra semi-colon can make a world of
> difference (brought down a phone system a few years ago).
>
> So yes, the labelling DOES make a difference. Whereas a Book is a Book,
> where it is used does change its meaning. So in Map<Book,Date>, Book is
> a key and in Comparator<Book>, Book is a Type.
>
> Otherwise the Javadoc author would not have made that distinction.
>
> It is used differently. As a key, it must provide its own comparison
> methodology. As a type, the Comparator makes the comparison, possibly
> using an external conversion such as I18N.

I can only guess that your definition of "key" is unlike any
I've encountered before. And, as mentioned before, that you attach
entirely too much significance to the choice of a letter to name a
formal parameter. <Shrug.>

The rest of us will (when appropriate) use Comparators to key our
SortedMaps on non-Comparables, or to key them using something other
than their "natural order." You, I guess, will bemoan the impossibility
of what the rest of us are doing ...

--
Eric.Sosman(a)sun.com

From: Dr J R Stockton on 4 Nov 2009 16:58
In comp.lang.java.programmer message <mn.13c97d9bb78aa66e.70216(a)a.com>,
Mon, 2 Nov 2009 16:09:42, Wojtek <nowhere(a)a.com> posted:
>How would you sort timezones?
>
>I am trying to sort them according to their offset from UTC. I cannot
>use a TreeMap because there are many timezones with the same offset,
>which of course over-writes the previously put timezone.


There are only about 30 Time Zones, since by definition a Time Zone
consists of all places where the local Winter Time has the same
difference from GMT - see a Dictionary, such as
<http://en.wiktionary.org/wiki/time_zone>
<http://www.chambersharrap.co.uk/chambers/features/chref/chref.py/main?t
itle=21st&query=time+zone>
<http://www.merriam-webster.com/dictionary/time+zone>.

Time Zoning is not affected by Summer Time, except in the opinion of the
semi-literates who write operating systems and suchlike.

--
(c) John Stockton, nr London, UK. ?@merlyn.demon.co.uk Turnpike v6.05.
Web <URL:http://www.merlyn.demon.co.uk/> - w. FAQish topics, links, acronyms
PAS EXE etc : <URL:http://www.merlyn.demon.co.uk/programs/> - see 00index.htm
Dates - miscdate.htm estrdate.htm js-dates.htm pas-time.htm critdate.htm etc.
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