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Newsgroups: comp.lang.java.programmer
From: Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at>
Subject: Re: calling own methods from constructor
References: <slrnippkd9.phi.avl@gamma.logic.tuwien.ac.at> <alpine.DEB.2.00.1104062255160.1512@urchin.earth.li>
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Date: 07 Apr 2011 08:36:49 GMT
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Tom Anderson <twic@urchin.earth.li> wrote:
> On Wed, 6 Apr 2011, Andreas Leitgeb wrote:
>> Is there any *good* use of having the constructor call a method that 
>> actually *can* be overridden in a subclass? I mean, are there 
>> (non-anti)patterns of explicitly allowing subclasses to hook into 
>> base-class's construction?

> public abstract class Library {
>  	private List<Document> documents;
>  	protected Library() {
>  		documents = new ArrayList<Document>();
>  		Collection<String> titles = listDocuments();
>  		for (String title: titles) {
>  			Document doc = loadDocument(title);
>  			// do other preparatory stuff with the document
>  			documents.add(doc);
>  		}
>  	}
>  	protected abstract Collection<String> listDocuments();
>  	protected abstract Document loadDocument(String title);
> }
>
> public class FilesystemLibrary extends Library {
>  	// ...
> }
> [...]

Sorry, in my eyes, this is one of the anti-patterns.

> What are the alternatives?

It's hard to speculate about alternatives for an artificial example.

I'd say, that they exist for any reasonable specification of the problem,
and "back it up"(*) by declaring specifications for which no (or only
mindboggingly contrived) alternatives exist as unreasonable ;-)

(*): In German, we use double-quotes also to indicate tongue-in-cheek
formulations that aren't to be taken entirely literally/serious.
I've recently learned that they are not always thusly understood,
elsewhere.  Therefore this explanation. Is there any common markup
for it that would be recognized in the English-speaking world?