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POAlternatives to static methods in Java
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  1. POAlternatives to static methods in Java
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    copied!<p>I'm making a mini ORM for a Java program I'm writing... there is a class for each table in my db, all inheriting from <code>ModelBase</code>.</p> <p><code>ModelBase</code> is abstract &amp; provides a bunch of static methods for finding &amp; binding objects from the db, for example:</p> <pre><code>public static ArrayList findAll(Class cast_to_class) { //build the sql query &amp; execute it } </code></pre> <p>So you can do things like <code>ModelBase.findAll(Albums.class)</code> to get a list of all persisted albums. My problem is that in this static context, I need to get the appropriate sql string from the concrete class Album. I can't have a static method like </p> <pre><code>public class Album extends ModelBase { public static String getSelectSQL() { return "select * from albums.....";} } </code></pre> <p>because there is no polymorphism for static methods in Java. But I don't want to make <code>getSelectSQL()</code> an instance method in <code>Album</code> because then I need to create an instance of it just to get a string that is really static in behavior.</p> <p>At the moment, <code>findAll()</code> uses reflection to get the appropriate sql for the class in question:</p> <pre><code>select_sql = (String)cast_to_class.getDeclaredMethod("getSelectSql", new Class[]{} ).invoke(null, null); </code></pre> <p>But that's pretty gross. </p> <p>So any ideas? It's a general problem I'm having time and time again - the inability to specify abstract static methods in classes or interfaces. I know <em>why</em> static method polymorphism doesn't and can't work, but that doesn't stop me from wanting to use it time again!</p> <p>Is there any pattern/construct that allows me to ensure that concrete subclasses X and Y implement a class method(or failing that, a class constant!)?</p>
 

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