习惯了用C语言，在java中对链表的运用还是不太熟练。因为题目中给的两个链表都是非递减顺序，所以直接比较就行了，创建一个新的链，小的放进去，最后再把剩下的接上。代码：

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode mergeTwoLists(ListNode p, ListNode q) {
        ListNode head = new ListNode ();
        ListNode s = head;
        while ((p!=null)&(q!=null)) {
            if (p.val < q.val) {
                s.next = new ListNode(p.val);
                p = p.next;
            }
            else {
                s.next = new ListNode(q.val);
                q = q.next;
            }
            s = s.next;

        }
        if (p == null) {
            s.next = q;
        }
        else {
            s.next = p;
        }
        return head.next;
    }
}