Package and visibility

Question

I'm making an SDK and I'm trying to separate classes to different packages, those classes use some other shared classes. The issue is if I made the shared classes public everyone will be able to see them, not only my classes. What's the right way to make them only accessible by my application?

Example :

---

Package a MyClass1

Package b MyClass2

Package c public MySharedClass

---

Because c is public MySharedClass will be able to access it, but the issue is that it will also will be visible to the world, how could I prevent that?

Answer 1

Create a package that is documented as an internal package, not to be used by clients.

There is no way in Java to make a class public only for certain packages: It either is public for everyone or package-private (public only in the declared package).

I think there's a proposal for modules to allow better control in the visibility of classes, but we'll have to wait, at least, for Java 8.

Answer 2

The packages are all "public" in Java, what you can protect is the classes within a package. For limiting the visibility of a class to only a given package, declare it like this (without the public visibility modifier):

class MyClass {
    // ...
}

In that way, only the classes in the same package as MyClass will be able to see it.