扩展包含对自身列表的引用的类

Question

I have a super class something like

class SuperClass {
   private String name;
   private List<SuperClass> subList;
   //getter setters
}

And I want to extend this SuperClass to have few more field, something like

class SubClass extends SuperClass {
    private String email;
   //getter setter
}

Now, my question is since the SuperClass holds a reference to a list of objects of type SuperClass, how will I ensure that any SubClass object holds a reference to a list of object of type SubClass... is it even possible? Am I doing something terribly wrong here?

EDIT Can I do something like

class SuperClass {
private String name;
private List<? extends SuperClass> subList;
public SuperClass(List<? extends SuperClass> subList) {
    this.subList = subList;
  }
}

And now SubClass just needs to call the constructor of super class

class SubClass extends SuperClass{
    private String email;

    private SubClass(List<? extends SuperClass> subList) {
        super(subList);
      }
    }

But Now if i want to add something to the list, I would not be able to because PECS (producer-extends, consumer-super) principle of generics doesn't allow me to do that.. So whenever, i'll have to add an object to subList I will have to create a new list and then set the list in SubClass

Answer 1

Would it be possible to introduce a third class? Something along those lines:

class AbstractClass<T> {
    protected List<T> subList;
    // getter setters
}

class SuperClass extends AbstractClass<SuperClass> {
    private String name;
    // getter setters
}

class SubClass extends AbstractClass<SubClass> {
    private String email;
    // getter setter
}

Answer 2

If you want to maintain that hierarchy, I would write something like this:

class SubClass extends SuperClass{
    ....
    public addItemToSublist(SuperClass item){
        if(item instanceof SubClass){
            subList.add(item);
        }
    }
}