swap nodes in pairs

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode swapPairs(ListNode head) {
        if (head == null){
            return null;
        }
        if (head.next == null){
            return head;
        }
        ListNode returnNode = head.next;
        ListNode nextNext = returnNode.next;
        returnNode.next = head;
        recSwap(nextNext, head);
        return returnNode;
    }

    public void recSwap(ListNode curr, ListNode temp){
        if (curr == null){
            temp.next = curr;
        } else if (curr.next == null){
            temp.next = curr;
        } else {
            ListNode next = curr.next;
            ListNode newCurr = next.next;
            next.next = curr;
            temp.next = next;
            recSwap(newCurr, curr);
        }
    }
}