Node is-a Position!
- Explain how Position is different from the Node (inner) class.
Here is how we declare the Node
class:
private static class Node<E> implements Position<E> {
Node<E> next;
Node<E> prev;
E data;
List<E> owner;
Node(E data, List<E> owner) {
this.data = data;
this.owner = owner;
}
@Override
public E get() {
return data;
}
}
Notice the attribute owner
. We use this attribute to check whether a "position" belongs to this data structure or not.
For example, when we insert to the front of the List:
public Position<T> insertFront(T data) {
Node<T> newFront = new Node<T>(data, this);
// update current front, head, tail, numElements, etc.
return newFront;
}
By passing this
to the constructor of Node
, we set "this data structure" to be the owner of newFront
.
We can then check if a given position belongs to this data structure:
public boolean first(Position<T> position) throws PositionException {
Node<T> node = (Node<T>) position;
if (node.owner != this) {
throw new PositionException();
}
return head == node;
}