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    <p>To restate the problem: you want your per-file-type classes to have statically available information on the type (e.g., name and description). </p> <p>We can easily get part-way there: create a separate class for your type info, and have a static instance of this (appropriately instantiated) in each per-file-type class.</p> <pre><code>package myFileAPI; public class TypeInfo { public final String name; public final String description; public TypeInfo(String name, String description) { this.name = name; this.description = description; } } </code></pre> <p>and, say:</p> <pre><code>package myFileAPI; public class TextFile { public static final TypeInfo typeInfo = new TypeInfo("Text", "Contains text."); } </code></pre> <p>Then you can do stuff like:</p> <pre><code>System.out.println(TextFile.typeInfo.name); </code></pre> <p>(Of course, you could also use getters in <code>TypeInfo</code> to encapsulate the underlying strings.)</p> <p>However, as you said, what we really want is to <em>enforce</em> the existence of a particular signature static method in all your per-file-type classes <em>at compile time</em>, but the 'obvious' design path leads to requiring an abstract static method in a common superclass which isn't allowed. </p> <p>We <em>can</em> enforce this <em>at run-time</em> though, which may be good enough to ensure it is coded correctly. We introduce a File superclass:</p> <pre><code>package myFileAPI; public abstract class File { public static TypeInfo getTypeInfo() { throw new IllegalStateException( "Type info hasn't been set up in the subclass"); } } </code></pre> <p>If <code>TextFile</code> now <code>extends File</code>, we will get this exception when calling <code>TextFile.getTypeInfo()</code> at runtime, unless TextFile has a same-signature method.</p> <p><strong>This is quite subtle</strong>: code with <code>TextFile.getTypeInfo()</code> in still compiles, even when there is no such method in TextFile. Even though static methods are bound at compile time, <em>the compiler can still look through the class hierarchy to determine the compile-time static call target</em>.</p> <p>So, we need code like:</p> <pre><code>package myFileAPI; public class TextFile extends File { private static final TypeInfo typeInfo = new TypeInfo("Text", "Contains text."); // Shadow the superclass static method public static TypeInfo getTypeInfo() { return typeInfo; } } </code></pre> <p>Note that we are still <strong>shadowing</strong> the superclass method, and so File.getTypeInfo() can still be 'meaninglessly' called.</p>
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    1. COThe accepted answer, and others, still didn't really address the intuitive design requirement that type info would be _statically_ available from the classes.
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    2. COThe first part effectively tweaks templatetypedef's answer. By 'You could also associate a type with each actual file you use by just having it store a FileType reference.', I'm assuming he meant a _static_ reference as I have done, but just didn't make that clear.
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    3. COmonsieurRigsby, thank you very much - I think this is really the best answer to my problem!
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