Groups > comp.lang.java.programmer > #3585

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

From	Jim Janney <jjanney@shell.xmission.com>
Newsgroups	comp.lang.java.programmer
Subject	Re: "Program to an interface" - When to break a design pattern
Date	2011-05-05 14:14 -0600
Organization	As little as possible
Message-ID	<2psjssq4zj.fsf@shell.xmission.com> (permalink)
References	<9dt5s6dalhetgfe99qs92c02hf0dbas44e@4ax.com>

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Zapanaz <http://joecosby.com/code/mail.pl@foo.com> writes:

> I've seen this design pattern before
>
> http://witte-consulting.com/documents/design-principles/
>
> and, in general, I see the point of it.
>
> But say we've got something like this
>
> LinkedHashMap<String, Integer> sortedMap = this.getSortedMap();
>
> So you have the method
>
> public LinkedHashMap<String, Integer> getSortedMap() {
>   //do stuff
> }
>
> (not necessarily public)
>
> Now the design principle says, the method signature should instead be
>
> public Map<String, Integer> getSortedMap() {
>   //do stuff
> }
>
> The problem is, where I'm creating sortedMap above, I need the map to
> retain the insertion order. If what's returned actually is a Map,
> rather than a LinkedHashMap, then the results the user actually sees
> are going to be in the wrong order. Making things worse, in this case,
> nothing would actually break, only the end user would notice anything
> was actually wrong.
>
> So in this case, it seems to me, that using LinkedHashMap in the
> method signature makes sense. The fact that the return retains the
> insertion order is an integral part of what the method does.
>
> If nothing else, it's going to save Fred Developer down the line from
> looking at the code around this
>
> Map<String, Integer> sortedMap = this.getSortedMap();
>
> and thinking "wait, how do I know getSortedMap() is going to return a
> result with the right ordering?", and having to waste time digging
> into that method.
>
> ***
>
> Opinions? Angry mob with torches and pitchforks? The Spanish
> Inquisition?

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 :-)

-- 
Jim Janney

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Thread

"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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