Convert between types based on the implementation of the same interface

Question

How to build a linked list which should store Elements of a given interface ( Sortable )?

The interfaces to build on is:

public interface Sortable<T>

My implemementation of the list is called public class DoublyLinkedList which stores data in nodes of the class public class DoublyLinkedListElement implements Sortable<Object>

So far so good. However there is another class public class Product implements Sortable<Product> .

Is it possible to use Methods of DoublyLinkedList to add objects of the type Product to a DoublyLinkedList without converting the type to DoublyLinkedListElement . If I try so I receive actual argument Product cannot be converted to DoublyLinkedListElement by method invocation conversion .

Answer 1

I'm not positive I understand the problem but I think what you need to do is make your add method take type Sortable. Then you do not have to cast anything and you would be able to add Product or DoublyLinkedListElement.

DoubleLinkedList<Sortable> list = new DoublyLinkerList<Sortable>();
list.add(new Product());
list.add(new DoublyLinkedListElement());

Answer 2

I hesitate answering this question in full; but as generics are an acquired taste, maybe something like:

public class DoublyLinkedList<T extends Sortable<T>> {
    private Element<T> first;
    private Element<T> last;
}

class Element<T extends Sortable<T>> {
    private T value;
    private Element<T> previous;
    private Element<T> next;
}