java - Recursive merge sort of two Linked Lists using third reference -

i trying solve recursive merge sort using third reference. wanted take third reference , keep on linking nodes 2 linked lists (two linked lists individually sorted) in sorted order without creation of node.

i see there recursive program referenced here. wanted try using third reference keep on messing up. let me know condition missing here?

import java.util.arraylist; import java.util.listiterator;  public class mergelinkedlistsintoexisting {     public static void main(string[] args){         node nodelist1 = null, nodelist2 = null;         node temp = null;         arraylist<integer> array1 = new arraylist<integer>();         array1.add(3);         array1.add(7);         array1.add(9);          arraylist<integer> array2 = new arraylist<integer>();         array2.add(1);         array2.add(2);         array2.add(8);          nodelist1 = add(nodelist1, array1);         nodelist2 = add(nodelist2, array2);         system.out.println("**list 1**");         print(nodelist1);         system.out.println("**list 2**");         print(nodelist2);         system.out.println("sorted list");         node nodelist3 = mergetwolists(nodelist1, nodelist2, temp);         print(nodelist3);     }     private static node add(node node, arraylist<integer> list){         node current = node;         node head = node;         listiterator<integer> = list.listiterator();         while(it.hasnext()){             if(head==null){                 head = new node();                 head.data = it.next();                 head.next=null;                 node = head;             }             else{                 current = new node();                 current.data = it.next();                 current.next = null;                 node.next = current;                 node = node.next;             }         }         return head;     }      private static void print(node node) {         if(node!=null){             while(node.next!=null){                 system.out.print(node.data + " ");                 node = node.next;             }             system.out.println(node.data);         }         else{             system.out.println("no elements in linkedlist.");         }     }       private static node mergetwolists(node nodelist1, node nodelist2, node temp) {         if(nodelist1 == null) return nodelist2;         if(nodelist2 == null) return nodelist1;          if(nodelist1.data <= nodelist2.data){             if(temp == null){                 temp = nodelist1;                 temp.next = mergetwolists(nodelist1.next, nodelist2, temp.next);             }             else{                 system.out.println(temp.data);                 temp.next = mergetwolists(nodelist1.next, nodelist2, temp.next);             }         }else{             if(temp == null){                 temp = nodelist2;                 system.out.println(temp.data);                 temp.next = mergetwolists(nodelist1, nodelist2.next, temp.next);             }             else{                 system.out.println(temp.data);                 temp.next = mergetwolists(nodelist1, nodelist2.next, temp.next);             }         }         return temp;     } } 

the resolution should temp.next in recursive call of mergetwolists. correct me , approach required.

edit: looked @ again, , think main modification fixed code removing special cases temp equals null.

i modified code , got working. pass through temp instead of temp.next, , don't need special case if temp null.

import java.util.arraylist; import java.util.listiterator;  public class mergelinkedlistsintoexisting {     public static void main(string[] args){         node nodelist1 = null, nodelist2 = null;         node temp = null;         arraylist<integer> array1 = new arraylist<integer>();         array1.add(3);         array1.add(7);         array1.add(9);          arraylist<integer> array2 = new arraylist<integer>();         array2.add(1);         array2.add(2);         array2.add(8);          nodelist1 = add(nodelist1, array1);         nodelist2 = add(nodelist2, array2);         system.out.println("**list 1**");         print(nodelist1);         system.out.println("**list 2**");         print(nodelist2);         system.out.println("sorted list");         node nodelist3 = mergetwolists(nodelist1, nodelist2, temp);         print(nodelist3);     }     private static node add(node node, arraylist<integer> list){         node current = node;         node head = node;         listiterator<integer> = list.listiterator();         while(it.hasnext()){             if(head==null){                 head = new node();                 head.data = it.next();                 head.next=null;                 node = head;             }             else{                 current = new node();                 current.data = it.next();                 current.next = null;                 node.next = current;                 node = node.next;             }         }         return head;     }      private static void print(node node) {         if(node!=null){             while(node.next!=null){                 system.out.print(node.data + " ");                 node = node.next;             }             system.out.println(node.data);         }         else{             system.out.println("no elements in linkedlist.");         }     }       private static node mergetwolists(node nodelist1, node nodelist2, node temp) {         if(nodelist1 == null) return nodelist2;         if(nodelist2 == null) return nodelist1;          if(nodelist1.data <= nodelist2.data){            temp = nodelist1;           temp.next = mergetwolists(nodelist1.next, nodelist2, temp);          }else{            temp = nodelist2;           temp.next = mergetwolists(nodelist1, nodelist2.next, temp);                         }         return temp;     } }  public class node{     int data;     node next; }