Question

On different sites, i was looking for programme in java doing reversing the order
of linked list(Singly Linked List and and doubly linked list) .I landed up on different sites like

1)http://geek-o-pedia.blogspot.com/2007/07/how-would-you-reverse-singly-linked.html
2)http://stackoverflow.com/questions/354875/reversing-a-linked-list-in-java-recursively

PointA-As per my understanding these programmes(take link 1) are good when you are writing your linked list class as the
programme is assuming we can access Node class which we can not(As its is private inner class in Linked List.)

Point B-Apart from that this programme will permanently reverse the order of Source linked list. So when we iterate on this
we will always get the elemts in reverse order.

Please let me know if both the above points are correct

So i tried to do it myself

–Reversing the singly Linked List

LinkedList list1 = new LinkedList();
    list1.add(1);
    list1.add(2);
    list1.add(3);
    list1.add(4);
    list1.add(5);

LinkedList reverseList1 = new LinkedList();

int size= list1.size();

// below loop will revrse the order of source linked list i.e list1

for(int i =size-1;i>=0;i--)
{
reverseList1.add(size-i-1, list1.get(i));
}

Just wanted to ensure if above approach is correct as i could not find these approach on internet which i found very simple .Everywhere i could find the approach similar to link1 and link2

posted at https://forums.oracle.com/forums/thread.jspa?threadID=2271413&tstart=0 too but did not get proper answer.

Answer 1

This seems like it would work fine. However, there is no need for the 1st parameter for the add method – add already inserts at the end (and you can also use addLast, which is identical).

Also, using get(i) that many times isn’t efficient. I would iterate over the first list (with foreach or with an iterator – , and for each element call addFirst.

Alternatively, use Collections.reverse, as panzerschreck suggested, which really is the best way IMO.