Lista Doblemente Enlazada - Insertar antes o después de un nodo

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