How to hide the internal structure of the Java API to the rest of the world

I'm developing a Java API to do things (secret, uh, them)

Is there any way to hide classes and the internal structure of APIs?

I have found so far:

>Use internal classes (ugly way, I don't want to put them all in the class file) > all classes are in one package so that I can use "package" - visibilty (also ugly, I need more packages)

Example:

---
package net.my.app;
//this is the Public Access
class MyPublicClass{
    public void somePublicFunction(){ 
        //access to not visibil classes
    }
}

---
package net.my.app.notvisible:
//this is what i want to hide
class MyNOTPublicClass{
    ...
}
---

Any ideas? thank you!

Solution

>Use the interface to define your

About this comment:

One way to implement my second bullet is to use a service to find classes, such as

public class Lookup {
    private static final Foo foo = new FooImpl();
    public static Foo getFoo() { 
        return foo; 
    }
}

Foo is an interface and fooimpl is an implementation class (it can be private if you want to force it not to be instantiated by the client)