Hiding classes in a jar file

Question

Is it really impossible to hide some classes in a jar file?

I wanted not to allow direct instantiation of the classes to keep it more flexible. Only the factory (or a facade) should be visible of this jar.

Is there any other way than solve this problem than creating two projects? (Two projects: the first one contains the classes (implementation) and the other one references to the first one and contains the factory; later only the second one will be referenced)

Answer 1

If I understand your question correctly, you would like to make sure that users of your library are forced to use your factory to instantiate their objects rather than using the constructors themselves.

As I see it there are two possibilities, one of which is silly but usable in few, specific cases, and the other one is the most practical and probably most commonly used way of doing it.

1. You could make all your classes into private inner classes of the factory. This would work if you had one factory per class, but is hardly workable if you have a lot of different classes being managed through one factory.
2. You could use the protected access modifier to restrict access to your class constructors. This is common practice when using the factory pattern.

Answer 2

Obfuscation can help you somehow.