public class DoublyLinkedList {
  private DLLElement head;
  private DLLElement tail;
  private DLLElement actual;

  public DoublyLinkedList() {

  }

  public void insertFirst(Object o) {
    DLLElement newFirstElem = new DLLElement();
    newFirstElem.setObject(o);

    if (head == null) {
      head = newFirstElem;
    } else {
      newFirstElem.setNext(head);
      head.setPrevious(newFirstElem);
      head = newFirstElem;
    }
  }

  public void insertLast(Object o) {
    if (head == null) {
      this.insertFirst(o);
      return;
    }

    DLLElement current = head;

    while (current.getNext() != null) {
      current = current.getNext();
    }

    DLLElement newFirstElem = new DLLElement();
    newFirstElem.setObject(o);

    // = last item of list
    current.setNext(newFirstElem);
    newFirstElem.setPrevious(current);
  }

  public void remove(Object o) {
    DLLElement current = head;

    while (current != null) {
      if (current.getObject().equals(o)) {
        if (current.getPrevious() != null) {
          current.getPrevious().setNext(current.getNext());
        } else {
          head = current;
        }

        if (current.getNext() != null) {
          current.getNext().setPrevious(current.getPrevious());
        }

        return;
      }

      current = current.getNext();
    }
  }

  public String toString() {
    String res = "[";

    DLLElement current = head;

    while (current != null) {
      res += current.getObject().toString() + ",";
      current = current.getNext();
    }

    return res.substring(0, res.length() - 1) + "]";
  }
}