If I want to create method insertMiddle(E e) what should i do? (DoublyLinkedList)?

Question

first of all, i tried to create a inserMiddle(E e) method in Generic type at doublyLinkedList class;
Assume the list has even number of nodes.

    public void insertMiddle(E e) {
    NodeDoubly current = header;
    NodeDoubly middle = new NodeDoubly(e);
    for(int i =0; i < size()/2 -1 ;i++) {
        current = current.next;
    }
    middle.next = current.next.next;
    middle.prev = current.next;
    size++;
   }