public int indexOf(Object inputData) {
        ListNode currentNode = this.firstNode;
        int position = 0;
        boolean found = false;

        for (; ; position++) {
            if (currentNode == null) {
                break;
            }

            if (inputData.equals(currentNode.getData())) {
                found = true;
                break;
            }

            currentNode = currentNode.getNext();
        }

        if (!found) {
            position = -1;
        }

        return position;
    }