I know recursive is easy to understand, but I still try a clear loop method :)

```
public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
ListNode fakeHead = new ListNode(0);
ListNode current = fakeHead;
while (l1 != null && l2 != null) {
if (l1.val <= l2.val) {
current.next = l1;
l1 = l1.next;
} else {
current.next = l2;
l2 = l2.next;
}
current = current.next;
}
if (l1 == null) current.next = l2;
if (l2 == null) current.next = l1;
return fakeHead.next;
}
```