Merge a linked list into another linked list at alternate positions in java

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Java

Given two linked lists, insert nodes of second list into first list at alternate positions of first list.

eg. Given two lists: 1->5->7->3->9 and 6->10->2->4, the first list should become 1->5->6->10->7->3->2->4->9 and second list should become empty.

If the first list is 1->2->3 and second list is 4->5->6->7, then first list should become 1->2->4->5->3->6>7

here is what I have :

public SLL joinLists(SLL in) {

    //SLL<e> res = new SLL<e>();
    SLLNode<e> tmp1=this.getFirst(); 
    SLLNode<e> tmp2= in.getFirst();

    while(tmp1.succ!=null && tmp2.succ!=null){
        tmp1 = tmp1.succ;
        this.insertAfter(tmp2.element,tmp1);
        tmp1=tmp1.succ;
        if(tmp2.succ!=null){
            tmp2 = tmp2.succ;
            this.insertAfter(tmp2.element,tmp1);
            tmp1=tmp1.succ;        
        }
        if(tmp1.succ!=null)
            tmp1=tmp1.succ;        
    }

    while(tmp2!=null){
        this.insertAfter(tmp2.element,tmp1);
            tmp1=tmp1.succ;
    }
    return this;
}