java - How is sortingPtr variable getting updated in the code below? -

need understand how sortingptr variable getting updated.

public class mergesortedlinkedlists {          public static node mergelinkedlists(node head1, node head2, node mergedhead){             node sortingptr = null;             if(head1 == null && head2 != null){                 return head2;             }             if(head1 == null && head2 == null){                 return mergedhead;             }             while(head1 != null && head2 != null){                 system.out.println("head1.data - " + head1.data);                 system.out.println("head2.data - " + head2.data);                 system.out.println("sortingptr - " + sortingptr);                 /*while(sortingptr != null){                     system.out.print("sortingptr.data - " + sortingptr.data + " ");                     sortingptr = sortingptr.next;                 }*/                 system.out.println();                 if(head1.data < head2.data){                     system.out.println("head1 < head2");                     if(mergedhead != null){                         mergedhead.next = head1;                         mergedhead = head1;                     } else{                         sortingptr = head1;                         mergedhead = head1;                     }                     head1 = head1.next;                 } else{                     system.out.println("head2 < head1");                     if(mergedhead != null){                         mergedhead.next = head2;                         mergedhead = head2;                     } else{                          sortingptr = head2;                         mergedhead = head2;                     }                     head2 = head2.next;                 }             }              if(head1 == null){                 mergedhead.next = head2;             }             if(head2 == null){                 mergedhead.next = head1;             }             return sortingptr;         }          public static void main(string[] args) {             singlylinkedlist linkedlist1 = new singlylinkedlist();             linkedlist1.head = linkedlist1.new node(10);             linkedlist1.head.next = linkedlist1.new node(50);             linkedlist1.head.next.next = linkedlist1.new node(70);             linkedlist1.head.next.next.next = linkedlist1.new node(90);             linkedlist1.head.next.next.next.next = linkedlist1.new node(100);              singlylinkedlist linkedlist2 = new singlylinkedlist();             linkedlist2.head = linkedlist2.new node(20);             linkedlist2.head.next = linkedlist2.new node(30);             linkedlist2.head.next.next = linkedlist2.new node(40);             linkedlist2.head.next.next.next = linkedlist2.new node(60);             linkedlist2.head.next.next.next.next = linkedlist2.new node(80);              singlylinkedlist mergedlist = new singlylinkedlist();             mergedlist.head = null;             mergedlist.head = mergelinkedlists(linkedlist1.head, linkedlist2.head, mergedlist.head);              node head = mergedlist.head;             while(head != null){                 system.out.print(head.data + " ");                 head = head.next;             }         }     }      class singlylinkedlist{         node head;         class node{             int data;             node next;              node(int data){                 this.data = data;                 next = null;             }         }     } 

i trying merge 2 sorted linked lists. method mergelinkedlists returning head of merged list in sortingptr variable. want understand how sortingptr variable getting updated return head of merged list in code mentioned above.

else{                         sortingptr = head1;                         mergedhead = head1;                     } 

and

else{                          sortingptr = head2;                         mergedhead = head2;                     } 

these block of codes ensure when mergedhead null(i.e. merging process has not started) set value of sortingptr value of mergedhead