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Re: "Program to an interface" - When to break a design pattern

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On 11-05-05 07:02 PM, Daniele Futtorovic wrote:
> On 05/05/2011 23:02, Jim Janney allegedly wrote:
>> Daniele Futtorovic<da.futt.news@laposte-dot-net.invalid>  writes:
>>
>>> On 05/05/2011 22:42, Jim Janney allegedly wrote:
>>>> Daniele Futtorovic<da.futt.news@laposte-dot-net.invalid>   writes:
>>>>
>>>>> On 05/05/2011 22:14, Jim Janney allegedly wrote:
>>>>>> The point of programming to the interface is to make it easier to
>>>>>> substitute a different implementation, which implies that any
>>>>>> reasonable implementation can be used.  If this is not true, if the
>>>>>> code that uses the object relies on behavior only found in one
>>>>>> implementation, then there is no benefit to using the interface, and
>>>>>> you make it more inviting for someone to break things later on.  So
>>>>>> in this case, no, programming to the interface would be the wrong
>>>>>> thing to do.  The point of design principles is to make you think
>>>>>> before you break them :-)
>>>>>
>>>>> Entirely disagreed. The code shown did not contain any
>>>>> justification for
>>>>> breaking the pattern in question, and on the opposite, it contained
>>>>> all
>>>>> the reasons to think more about encapsulation, which is the true
>>>>> underlying rationale for coding to interfaces -- not polymorphism
>>>>> per se.
>>>>
>>>> The justification is not in the code shown, but in the accompanying
>>>> remark "I need the map to retain the insertion order."  There's no
>>>> interface in the JRE that promises this, and only one class that
>>>> provides it, which makes encapsulation, shall we say, difficult.
>>>
>>> That's not the point! Yes, you need a LinkedHashMap to retain
>>> insertion order in a Map. But retaining insertion order is
>>> relevant... only when inserting.
>>
>> Think a minute.  When does retaining insertion order actually matter?
>> When you build the map, or some time later when you iterate over it?
>> Hint: if you never iterate over it, the order doesn't matter at all.
> 
> I don't need a full minute to see that this is even further beside the
> point.

Yeah, as in, your argument is incorrect, and Jim is right.

You see this bit from the LinkedHashMap API?:

"This implementation spares its clients from the unspecified, generally
chaotic ordering provided by HashMap (and Hashtable), without incurring
the increased cost associated with TreeMap. It can be used to produce a
copy of a map that has the same order as the original, regardless of the
original map's implementation."

"Spares its _clients_". You provide this implementation for the
_clients_. Just any Map won't do, Daniele. And if you "program to the
interface" blindly, and return a Map from this method, then as long as
the OP's _unchanged_ code is used to implement

public Map<String, Integer> getSortedMap()

then we'll get a LinkedHashMap and obey the desired contract. But down
the road - since we've failed to specify the requirement - things could
change, and the original implementation requirement be violated. In fact
a maintainer will look at the method's return type, and the
(unfortunate) name of te method, and in the absence of design
documentation decide maybe to use a SortedMap implementation instead.
*Which would be a mistake*...but your recommended approach would
encourage him to do it.

Don't get all blinded by design principles like "program to the
interface". Most of the things you access in a real-world complex
application are exposed through classes, not interfaces.

AHS

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"Program to an interface" - When to break a design pattern Zapanaz <http://joecosby.com/code/mail.pl@foo.com> - 2011-05-05 12:21 -0700
  Re: "Program to an interface" - When to break a design pattern Joshua Cranmer <Pidgeot18@verizon.invalid> - 2011-05-05 15:43 -0400
    Re: "Program to an interface" - When to break a design pattern Lew <noone@lewscanon.com> - 2011-05-05 17:19 -0400
  Re: "Program to an interface" - When to break a design pattern Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2011-05-05 21:47 +0200
  Re: "Program to an interface" - When to break a design pattern Jim Janney <jjanney@shell.xmission.com> - 2011-05-05 14:14 -0600
    Re: "Program to an interface" - When to break a design pattern Zapanaz <http://joecosby.com/code/mail.pl@foo.com> - 2011-05-05 13:26 -0700
    Re: "Program to an interface" - When to break a design pattern Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2011-05-05 22:27 +0200
      Re: "Program to an interface" - When to break a design pattern Jim Janney <jjanney@shell.xmission.com> - 2011-05-05 14:42 -0600
        Re: "Program to an interface" - When to break a design pattern Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2011-05-05 22:48 +0200
          Re: "Program to an interface" - When to break a design pattern Jim Janney <jjanney@shell.xmission.com> - 2011-05-05 15:02 -0600
            Re: "Program to an interface" - When to break a design pattern Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2011-05-06 00:02 +0200
              Re: "Program to an interface" - When to break a design pattern Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-05-05 19:49 -0300
                Re: "Program to an interface" - When to break a design pattern Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2011-05-06 02:28 +0200
                Re: "Program to an interface" - When to break a design pattern Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-05-06 07:24 -0300
                Re: "Program to an interface" - When to break a design pattern Patricia Shanahan <pats@acm.org> - 2011-05-06 07:03 -0700
                Re: "Program to an interface" - When to break a design pattern Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-05-06 17:30 -0300
                Re: "Program to an interface" - When to break a design pattern Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2011-05-06 18:56 +0200
                Re: "Program to an interface" - When to break a design pattern Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-05-06 17:50 -0300
                Re: "Program to an interface" - When to break a design pattern Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2011-05-06 23:37 +0200
                Re: "Program to an interface" - When to break a design pattern Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-05-06 19:43 -0300
              Re: "Program to an interface" - When to break a design pattern Jim Janney <jjanney@shell.xmission.com> - 2011-05-05 17:17 -0600
                Re: "Program to an interface" - When to break a design pattern Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2011-05-06 02:28 +0200
          Re: "Program to an interface" - When to break a design pattern Zapanaz <http://joecosby.com/code/mail.pl@foo.com> - 2011-05-05 23:25 -0700
            Re: "Program to an interface" - When to break a design pattern Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2011-05-06 18:25 +0200
              Re: "Program to an interface" - When to break a design pattern Zapanaz <http://joecosby.com/code/mail.pl@foo.com> - 2011-05-07 16:26 -0700
                Re: "Program to an interface" - When to break a design pattern Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2011-05-08 03:28 +0200
                Re: "Program to an interface" - When to break a design pattern Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-05-08 00:05 -0300
                Re: "Program to an interface" - When to break a design pattern Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2011-05-08 16:15 +0200
                Re: "Program to an interface" - When to break a design pattern Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-05-08 14:20 -0300
                Re: "Program to an interface" - When to break a design pattern Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2011-05-08 19:48 +0200
                Re: "Program to an interface" - When to break a design pattern markspace <-@.> - 2011-05-10 07:36 -0700
                Re: "Program to an interface" - When to break a design pattern Jim Janney <jjanney@shell.xmission.com> - 2011-05-10 13:04 -0600
                Re: "Program to an interface" - When to break a design pattern Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2011-05-10 21:31 +0200
                Re: "Program to an interface" - When to break a design pattern Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-05-10 20:01 -0300
                Re: "Program to an interface" - When to break a design pattern Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2011-05-11 19:14 +0200
                Re: "Program to an interface" - When to break a design pattern Patricia Shanahan <pats@acm.org> - 2011-05-11 10:41 -0700
                Re: "Program to an interface" - When to break a design pattern Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2011-05-11 19:55 +0200
                Re: "Program to an interface" - When to break a design pattern Lew <noone@lewscanon.com> - 2011-05-11 16:42 -0400
                Re: "Program to an interface" - When to break a design pattern Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2011-05-11 23:34 +0200
                Re: "Program to an interface" - When to break a design pattern "John B. Matthews" <nospam@nospam.invalid> - 2011-05-12 00:51 -0400
                Re: "Program to an interface" - When to break a design pattern Lew <noone@lewscanon.com> - 2011-05-12 00:58 -0400
                Re: "Program to an interface" - When to break a design pattern Tom Anderson <twic@urchin.earth.li> - 2011-05-12 20:08 +0100
        Re: "Program to an interface" - When to break a design pattern Lew <noone@lewscanon.com> - 2011-05-05 17:24 -0400
          Re: "Program to an interface" - When to break a design pattern Jim Janney <jjanney@shell.xmission.com> - 2011-05-05 16:00 -0600
          Re: "Program to an interface" - When to break a design pattern Jukka Lahtinen <jtfjdehf@hotmail.com.invalid> - 2011-05-06 15:01 +0300
            Re: "Program to an interface" - When to break a design pattern Lew <noone@lewscanon.com> - 2011-05-06 12:17 -0400
              Re: "Program to an interface" - When to break a design pattern Zapanaz <http://joecosby.com/code/mail.pl@foo.com> - 2011-05-07 16:28 -0700
    Re: "Program to an interface" - When to break a design pattern Lew <noone@lewscanon.com> - 2011-05-05 17:21 -0400
      Re: "Program to an interface" - When to break a design pattern Jim Janney <jjanney@shell.xmission.com> - 2011-05-05 15:58 -0600
        Re: "Program to an interface" - When to break a design pattern Lew <noone@lewscanon.com> - 2011-05-05 18:18 -0400
      Re: "Program to an interface" - When to break a design pattern Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-05-05 19:20 -0300
        Re: "Program to an interface" - When to break a design pattern Lew <noone@lewscanon.com> - 2011-05-05 18:23 -0400
          Re: "Program to an interface" - When to break a design pattern Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-05-05 20:17 -0300
  Re: "Program to an interface" - When to break a design pattern Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-05-05 18:26 -0300
  Re: "Program to an interface" - When to break a design pattern Steven Simpson <ss@domain.invalid> - 2011-05-05 22:57 +0100
    Re: "Program to an interface" - When to break a design pattern Tom Anderson <twic@urchin.earth.li> - 2011-05-05 23:29 +0100
      Re: "Program to an interface" - When to break a design pattern Steven Simpson <ss@domain.invalid> - 2011-05-06 13:30 +0100
        Re: "Program to an interface" - When to break a design pattern Lew <noone@lewscanon.com> - 2011-05-06 12:19 -0400
    Re: "Program to an interface" - When to break a design pattern Jim Janney <jjanney@shell.xmission.com> - 2011-05-05 16:41 -0600
      Re: "Program to an interface" - When to break a design pattern Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-05-05 20:47 -0300
  Re: "Program to an interface" - When to break a design pattern Roedy Green <see_website@mindprod.com.invalid> - 2011-05-05 16:41 -0700
    Re: "Program to an interface" - When to break a design pattern Jim Janney <jjanney@shell.xmission.com> - 2011-05-05 22:47 -0600
    Re: "Program to an interface" - When to break a design pattern Zapanaz <http://joecosby.com/code/mail.pl@foo.com> - 2011-05-05 23:28 -0700
  Re: "Program to an interface" - When to break a design pattern Michal Kleczek <kleku75@gmail.com> - 2011-05-06 17:15 +0200
    Re: "Program to an interface" - When to break a design pattern Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-05-06 20:53 -0300
      Re: "Program to an interface" - When to break a design pattern Lew <noone@lewscanon.com> - 2011-05-06 21:39 -0400
        Re: "Program to an interface" - When to break a design pattern Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-05-07 00:56 -0300
      Re: "Program to an interface" - When to break a design pattern Michal Kleczek <kleku75@gmail.com> - 2011-05-08 12:24 +0200
        Re: "Program to an interface" - When to break a design pattern Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-05-08 13:42 -0300
          Re: "Program to an interface" - When to break a design pattern Michal Kleczek <kleku75@gmail.com> - 2011-05-09 11:04 +0200
            Re: "Program to an interface" - When to break a design pattern Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-05-09 19:33 -0300
              Re: "Program to an interface" - When to break a design pattern Michal Kleczek <kleku75@gmail.com> - 2011-05-10 15:51 +0200
                Re: "Program to an interface" - When to break a design pattern Jim Janney <jjanney@shell.xmission.com> - 2011-05-10 13:15 -0600
                Re: "Program to an interface" - When to break a design pattern Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-05-10 19:40 -0300

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