CODEWITHSUNDEEP
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Josephine
Josephine

Reputation: 261

Doubly Linked List Null Pointer Exception

I'm trying to work on a remove function for a doubly linked list, but I keep getting a Null Pointer exception on the current.prev.next = current.next; part. I don't think I really understand what a null pointer exception is, because I have no idea what to do to fix this. The log function is just one I wrote to write to an output file, and retval[1] is the element I'm searching to delete.

Node current = head;

    while(current != null)
    {
            if((current.data).compareTo(retval[1]) == 0)
            {
                    if(current.prev == null)
                        head = current.next;

                    if(current.next == null)
                        tail = current.prev;

                    current.prev.next = current.next;
                    current.next.prev = current.prev;

                    current = null;

                    valid++;
                    log(line + "\n" + "Sucsessfully Removed \n");

            }
            else
            {
                log(line + "\n" + InvalidTransaction + " - Element does not exist \n");     
            }

            current = current.next;
        }

I'm sure it's something stupid, but I don't know what it is. Any help would be greatly appreciated.

Upvotes: 0

Views: 2610

Answers (2)

Vinod Kumar Y S
Vinod Kumar Y S

Reputation: 628

Just replace 

current.prev.next = current.next;
current.next.prev = current.prev;

with

if(null != current.prev) current.prev.next = current.next;
if(null != current.next) current.next.prev = current.prev;

And also you need to break the loop once the element is found.

Upvotes: 1

tbodt
tbodt

Reputation: 16987

A NullPointerException means that you tried to do something with an object that was null. Since current definitely wasn't null, then current.prev must have been null. Go from there.

Upvotes: 0

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