public interface packageA.MyInterface {
    protected void methodA();
}
 
public class packageB.MyClass implements packageA.Interface {
    protected void methodA() {
        //...
    }
    //who should have access to this mehtod? Members of packageA od members of packageB?
}
 
A similar problem would occour if the interface itself would be protected
 
protected interface packageA.MyInterface {
    public void methodA();
}
public class packageA.MyClass1 implements packageA.Interface {
    public void methodA() {
    }
}
 
public class packageB.MyClass2 extends packageA.MyClass1 {
    
}
//This class would actually implement an interface it is not allowed to implement.

public interface Unspeakable {
   public horrify();
}

public interface Unspeakable {
   horrify();
}

    public interface PublicInterface {
        public void publicMethod();
    }
    protected interface ProtectedInterface extends PublicInterface {
        public void protectedMethod();
    }