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From: Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid>
Newsgroups: comp.lang.java.programmer
Subject: Re: "Program to an interface" - When to break a design pattern
Date: Thu, 05 May 2011 21:47:56 +0200
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On 05/05/2011 21:21, Zapanaz allegedly wrote:
>
> 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?

Prodding with a cushion: not your goddamn business.

As far as the bit of code you showed is concerned, "the right ordering" 
is whatever you get passed. If you take input somewhere and need to 
retain passing order, then *your code* ought to work with a 
LinkedHashMap. But as for what you get passed, that's the responsibility 
of the passer -- within certain boundaries, of course: if it's invalid 
in some way, throw an Exception.

Incidentally, if it's a sorted map, you might as well declare it as a 
java.util.SortedMap. Which has an ordering, although it's not the same 
thing as a LinkedHashMap, of course.

-- 
DF.
An escaped convict once said to me:
"Alcatraz is the place to be"