public void switchPairs() {
    if (front == null) {
    }

    else {
        ListNode current = front;

        while (current.next.next != null) {
            int temp = current.data;
            current.data = current.next.data;
            current.next.data = temp;
            current = current.next.next;
        }
        if (current.next!=null) {
            int temp = current.data;
            current.data = current.next.data;
            current.next.data = temp;
        }
    }

}