java合并有序链表

public ListNode mergeTwoLists (ListNode l1, ListNode l2) {
	if (l1 == null) return l2;
	if (l2 == null) return l1;
	ListNode dummy = new ListNode(-1);
	ListNode temp = dummy;
	while(l1 != null && l2 != null) {
		if (l1.val <= l2.val) {
			temp.next = l1;
			l1 = l1.next;
		} else {
			temp.next = l2;
			l2 = l2.next;
		}
		temp = temp.next;
	}
	if (l1 != null) {
		temp.next = l1;
	}
	if (l2 != null) {
		temp.next = l2;
	}
	return dummy.next;
}