Lista Doblemente Enlazada - Insertar al inicio/fin, y eliminar nodo

//points to first node of list DNode first; //points to last node of list DNode last; public void insertBeginning(List<DNode> list, DNode newNode) { if (first == null) { first = newNode; last = newNode; newNode.previous = null; newNode.next = null; } else { insertBefore(list, last, newNode); } } public void insertEnd(List<DNode> list, DNode newNode) { if (last == null) { insertBeginning(list, newNode); } else { insertAfter(list, last, newNode); } } public void remove(DNode node) { if (node.previous == null) { first = node.next; } else if (node.next == null) { last = node.previous; } else { node.previous.next = node.next; node.next.previous = node.previous; }