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POOOP-Design: Interface-Methods with implementation-dependent parameters
 

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  1. POOOP-Design: Interface-Methods with implementation-dependent parameters
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    <p>The subject says it already: </p> <p>I am thinking right now about following design-problem: I define an interface for a specific type of object that contains various methods. Now i have the problem, that different implementations of this interface, need additional/different method-parameters (because the way they are implemented makes this necessary), which i cannot incorporate into the interface because they are not common to <em>all</em> interface-implementations.</p> <p>Now i realize that interface implementations could come with their own property-files, loading their additional parameters from there, but what if these parameters need to be passed in at runtime?</p> <p>Currently i can only think of passing in a <code>Map&lt;String, Object&gt; parameters</code> to overcome this problem - since JDK-Classes like <a href="http://docs.oracle.com/javase/6/docs/api/javax/xml/parsers/DocumentBuilderFactory.html" rel="nofollow">DocumentBuilderFactory</a> are doing something very similar by providing methods like <code>setAttribute(String attName, Object attValue)</code> this seems like a feasible approach to solve this problem. Nevertheless i would be interested in how others solve issues like this, alternative ideas?</p> <p>I dont want to derive from the interface and add additional methods, since in my case i would then have to throw <code>NotImplementException</code> from the methods of the base interface.</p> <p><strong>UPDATE</strong>:</p> <p>What could be eventual problems of the Map-approach? Implementing classes are free to ignore it completely if they cant make use of additional parameters. Others might check if the Map contains the desired parameter-names, check the type of their values and use them if valid, throw an exception if not. I have also seen this being used for the abstract class JAXBContext, so it seems to be a common approach..</p> <p><strong>UPDATE</strong>:</p> <p>I decided to go for the map-approach, since i dont see any obvious disadvantages and it is being used in the JDK as well (yes, i know this does not necessarily mean much :) Since i cannot accept an answer on this question, i will just upvote. Thanks for your input!</p> <p>regards,</p> <p>--qu</p>
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    1. COIs this information something a method will need or something the object needs to perform it's actions? Give a concrete example. Using **Map<String,Object>** is a horrible design decision.
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      1. USMaurício Linhares
    2. CO@MaurícioLinhares I realize that this solution is far from optimal (thats why i asked this question), but take the DocumentBuilderFactory as an example - the interface is identical for all possible DOM-Parsers, yet different DOM-Parser-Implementations offer different features/parameters which you could never all incorporate into the interface, yet you need a way to pass in those parameters somehow at runtime - i mentioned how the JDK solves this...
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    3. COThink about it, this is an **initialization** process. The factory sole purpose is to create a new object that is ready to do it's work, it's **interface** is not changed at all. What you want is something else, you want to add this to your **interface methods**. If what you want is really setup the object during initialization, make these objects constructor parameters and that is it.
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