Creating a plugin system for my app

Hi there,
I want to create a plugin system for my application, but I have no idea how to start. I've programmed C# before, and with that language I could dynamicly load .NET assemblies (.dll files), but how can I do such a thing in java? And I would like to let it work on al platforms.
Does anybody have a tutorial or something?
Thanks in advance.

In Java you can load classes and create objects from
dynamically loaded classes. The convention in Java is
that a plugin is a Java Bean (not to be confused with
Enterprise Java Bean, this is different). Search for
and read up on Java Beans. Also study the Class class.No, they don't have to be beans, but it makes life a lot easier if they
1) Have no-args constructors
2) Implement a known inteface, which characterises the behaviour the plugins will provide.
The interface will ofen include some kind of initialise method (as a substitute for constructor arguments).
The common interface is known at the time of compiling the framework, and new instances of the dynamically loaded classes are cast to it, and so become accessible.

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