Then why is the subject »Listing loaded classes«? Either you
 want to list loaded classes or classes from the classpath.

 A similar operation exists in the library »ram.jar«.
 This operation is based on Code by Ralf Ullrich.

 One can find all classes of a jar that have any chosen
 property, as long as this property can be obtained from the
 class reference.

 For example, to find all classes implementing »java.util.Map«,
 one sets a filter accepting only classes which
 »java.util.Map« is assignable from:

public boolean accepts( final java.lang.Class class_ )
{ return java.util.Map.class.isAssignableFrom( class_ ); }

 One also needs to provide a starting class to find the jar, which
 is done as follows.

public java.lang.String entryPath(){ return "java.lang.Object"; }

 The jar containing this type will be chosen for exploration.

 However, the client does not need to specify this »entryPath«,
 as "java.lang.Object" is the default obtained by extending
 »de.dclj.ram.java.lang.reflect.Finder.DefaultSpecification«.

 The example client is:

public class Main
{ /* based on an idea and on code by Ralf Ullrich from 2006 */

 public static void main( final java.lang.String[] args )
 { new de.dclj.ram.java.lang.reflect.Finder
   ( new de.dclj.ram.java.lang.reflect.Finder.DefaultSpecification()
     {  
       public boolean isClassFinder(){ return true; }

       public boolean accepts( final java.lang.Class class_ )
       { return java.util.Map.class.isAssignableFrom( class_ ); }

       }).inspectJar(); }}

class java.lang.ProcessEnvironment
class java.rmi.server.RemoteObjectInvocationHandler$MethodToHash_Maps$1
class java.security.AuthProvider
(...)
class java.util.Properties
class java.util.Hashtable
interface java.util.Map

 The library »ram.jar« is an early publication in alpha state,
 it is experimental, changing, and mostly undocumented. See:

http://www.purl.org/stefan_ram/pub/ram-jar

On Fri, 06 Jul 2007 11:15:42 +0200, Julien Lafaye
<sensei+usenet@pinglou.net> wrote, quoted or indirectly quoted someone
who said :

For a description of how to solve this see:
http://mindprod.com/projects/interfacefinder.html

It is one of the suggested student projects.  Maybe some day someone
will bite.

The other way to do it is with a properties file containing only the
classes you want considered.  Sell it as a feature.
--
Roedy Green Canadian Mind Products
The Java Glossary
http://mindprod.com

I suggest using an easier approach:
1) Make a standard folder for plugins, and load all the classes in it.
2) Register the plugin classes. There are two ways to do this:
  a) When loading the classes, check each one of them whether it
implements your interface.
  b) Put in the specification of plugins that they have to register
themselves in a class of yours while loading. In other words, every
plugin should call "YourRegisterClass.register(ThePluginClass)", and
your method will validate that they implement the interface, and store
them in a list or something. (I prefer this way.)