[OTHER] is there any one can explain why SinglyLinkedList extends Node?

### What would you like to share?

```java
public class SinglyLinkedList extends Node {
    private Node head;
    private int size;

    class Node {

    int value;
    Node next;
    }
}
```



### Additional information

I think `LinkedList and Node` is `has-a` relation, not `is-a`.

