Can I restrict inheritance to package without using 'default'?

Question

I have some classes that I need to be able to extend within the same package. But I don't want for anyone else outside of my package to extend my classes. Classes in other packages need to be able to call my classes so I cannot use 'default'.

Is there any way (maybe through an interface) that I can achieve this?

Answer 1

If you make your constructors package local, it can only be extended in the same package however public members can be accessed in any class if it is a public class.

Answer 2

I'd do this by creating a base class with default visibility, then extend it with a public final class that external classes can call into but not extend. For example:

class MyBase {
    public void doSomething() { ... }
}

public final class PublicBase extends MyBase { }

class ExtendedBase {
    @Override
    public void doSomething() { ... }
}