limiting access to a class's interface in java

I have situation where I have to restrict the access to a class. to further elaborate, I have two classes, say A and B that depend on class C, but A doesn't need to use the complete interface of C, the same goes to B. What I did was, make C implement two different interfaces, one interface A can access, the other for B to refer to. What I am doing here, is it correct? or should I just document this? or else is there a better approach?

To give more context, I am trying to implement an system which allows an interface for plug-ins. And I don't want someone accessing parts of a class I don't want them to.