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POHow to save and load different types of objects?
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copied!<p>During coding I frequently encounter this situation:</p> <ol> <li>I have several objects (<code>ConcreteType1</code>, <code>ConcreteType2</code>, ...) with the same base type <code>AbstractType</code>, which has abstract methods <code>save</code> and <code>load</code> . Each object can (and has to) save some specific kind of data, by overriding the <code>save</code> method. </li> <li>I have a list of <code>AbstractType</code> objects which contains various <code>ConcreteTypeX</code> objects.</li> <li>I walk the list and the <code>save</code> method for each object.</li> </ol> <p>At this point I think it's a good OO design. (Or am I wrong?) The problems start when I want to reload the data:</p> <p>Each object can load its own data, but I have to know the concrete type in advance, so I can instantiate the right <code>ConcreteTypeX</code> and call the <code>load</code> method. So the loading method has to know a great deal about the concrete types. I usually "solved" this problem by writing some kind of marker before calling <code>save</code>, which is used by the loader to determine the right <code>ConcreteTypeX</code>.</p> <p>I always had/have a bad feeling about this. It feels like some kind of anti-pattern...</p> <p>Are there better ways?</p> <p>EDIT: I'm sorry for the confusion, I re-wrote some of the text. I'm aware of serialization and perhaps there is some next-to-perfect solution in Java/.NET/yourFavoriteLanguage, but I'm searching for a general solution, which might be better and more "OOP-ish" compared to my concept.</p>

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