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POIs there a commonly used OO Pattern for holding "constant variables"?
 

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    <p>I am working on a little <a href="http://mirror.mit-ocw.sbu.ac.ir/OcwWeb/Electrical-Engineering-and-Computer-Science/6-170Fall-2005/Projects/index.htm" rel="nofollow noreferrer">pinball-game project</a> for a hobby and am looking for a pattern to encapsulate constant variables.</p> <p>I have a model, within which there are values which will be constant over the life of that model e.g. maximum speed/maximum gravity etc. Throughout the GUI and other areas these values are required in order to correctly validate input. Currently they are included either as references to a <code>public static final</code>, or just plain hard-coded. I'd like to encapsulate these "constant variables" in an object which can be injected into the model, and retrieved by the view/controller.</p> <p>To clarify, the value of the "constant variables" may not necessarily be defined at compile-time, they could come from reading in a file; user input etc. What is known at compile time is <em>which</em> ones are needed. A way which may be easier to explain it is that whatever this encapsulation is, the values it provides are <strong>immutable</strong>.</p> <p>I'm looking for a way to achieve this which: </p> <ul> <li>has compile time type-safety (i.e. not mapping a string to variable at runtime)</li> <li>avoids anything static (including enums, which can't be extended)</li> </ul> <p>I know I could define an interface which has the methods such as: </p> <pre><code> public int getMaximumSpeed(); public int getMaximumGravity(); </code></pre> <p>... and inject an instance of that into the model, and make it accessible in some way. However, this results in a lot of boilerplate code, which is pretty tedious to write/test etc (I am doing this for funsies :-)).</p> <p>I am looking for a better way to do this, preferably something which has the benefits of being part of a shared vocabulary, as with design patterns. </p> <p>Is there a better way to do this?</p> <p>P.S. I've thought some more about this, and the best trade-off I could find would be to have something like: </p> <pre><code>public class Variables { enum Variable { MaxSpeed(100), MaxGravity(10) Variable(Object variableValue) { // assign value to field, provide getter etc. } } public Object getVariable(Variable v) { // look up enum and get member } } // end of MyVariables </code></pre> <p>I could then do something like: </p> <pre><code>Model m = new Model(new Variables()); </code></pre> <p><em>Advantages</em>: the lookup of a variable is protected by having to be a member of the enum in order to compile, variables can be added with little extra code<br> <em>Disadvantages</em>: enums cannot be extended, brittleness (a recompile is needed to add a variable), variable values would have to be cast from Object (to Integer in this example), which again isn't type safe, though generics may be an option for that... somehow</p>
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    1. COWhat language is this in?
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    2. COFor me it's Java, but I would prefer if the concept would apply to any polymorphic, OO language, and not be "language x has this feature... though no other ones do." Even if the simple answer is "No", I'm happy with that :)
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