public void readToList(){
        Scanner scan = new Scanner(System.in);
        System.out.println("Please enter numbers to add to List. To stop, enter -9999");

        int newInt = scan.nextInt();

        while(newInt != -9999){
            pushNumber(newInt);
            newInt = scan.nextInt();
        }
        System.out.println("Done");

        mergeSort();

        IntNodeTwo pointer, prev = null;

        for(pointer=this._head; pointer !=null; pointer = pointer.getNext()){
            pointer.setPrev(prev);
            prev = pointer;
        }
        this._tail = prev;
    }

    private void mergeSort() {
            _head = mergeSort (_head);
        }

    private IntNodeTwo mergeSort (IntNodeTwo node) {

        if (node == null || node.getNext() == null)
            return node;

        IntNodeTwo list2 = split(node);
        node = mergeSort (node);
        list2 = mergeSort(list2);

        return merge(node, list2);
    }

    private IntNodeTwo split(IntNodeTwo node) {
        if (node == null || node.getNext() == null)
            return null;

        IntNodeTwo list2 = node.getNext();
        node.setNext (list2.getNext());
        list2.setNext (split(list2.getNext()));
        return list2;

    }

    private IntNodeTwo merge(IntNodeTwo list1, IntNodeTwo list2) {

        if (list1 == null)
            return list2;
        if (list2 == null)
            return list1;

        if (list1.getNum() < list2.getNum()) {
            list1.setNext(merge(list1.getNext(), list2));
            return list1;
        }

        else {
            list2.setNext(merge(list1, list2.getNext()));
            return list2;
        }
    }
}