This is a doubly-linked list implementation of the List interface that has a reference to the previous, and also to the next element in the list for each element. The class also implements the Deque interface. It is fairly cheap to insert or delete an element from the list because it needs only the adjustment of few references. On the other hand, the access to an element by index will need iteration from the start of the list, or from the end of the list, whichever is closer to the specified indexed element.