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POIf the factory pattern forces you to use default constructors then how should one design the class interface requiring parameterized constructors?
 

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  1. POIf the factory pattern forces you to use default constructors then how should one design the class interface requiring parameterized constructors?
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    <p>I have a set of DAOs (<a href="http://java.sun.com/blueprints/corej2eepatterns/Patterns/DataAccessObject.html" rel="nofollow">Data access objects</a>) that need to be fetched from a DAOFactory (using the factory-method pattern).</p> <p>Now we have the case that DAOs must always be initialized with parameters e.g.: (with String params)</p> <p><code>MyDataDAO myDAO = new myDAO("myProject", "myProjectWallName");</code></p> <p>Now, having a bunch of DAOs has required us to refactor (using the factory pattern) and here are the conflicting <em>forces</em>:</p> <ol> <li>If we refactor our DAOs to NOT use any default arguments (probably a good thing) we may land up having setters/getters for the mandatory members that MUST be initialized. Implying probably null checks/assertions littered all throughout (bad thing IMO)</li> <li>The other way is to force every method of the DAO to carry the corresponding mandatory arguments along with what they already have (too much data/long parameter list - probably bad but maybe the only choice?)</li> <li>Use Spring! Well we do for some of the purely stateless DAOs which really don't require any defaults to be set up. But I don't think Spring really supports run-time constructor-parameter initialization, since it creates and caches the objects at start-up. So back to square one (Spring may support this but I really haven't been able to find anything about this as yet. Help? :)</li> </ol> <p>So how should one go about designing a 'good' interface for the classes that are to be instantiated using a factory i.e., best practices to follow in this regard. I've always encountered the non-parameterized constructor case up until now where I do feel a valid need/reason for having the parameters. I personally feel it's <em>bad</em> OO to have a default constructor only and set everything through setters-getters, defeating the very purpose constructors exist to solve! </p> <p>Confused...</p>
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    1. CO@Bringer128 - It's not completely arbitrary. The type of parameters are already known and different for different type of DAOs.
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    2. CORead about the builder pattern. It helps particularly when you have higher number of context based input arguments and is a great alternative. Also, your factory can have multiple methods (one with no args can create a dao with default values.. or you can accept the arguments using the factory method).
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