Removing a node in a linked list

Question

Trying to remove a node by index now. I'd like to print out the list of nodes with indices so the user can select the index as seen. I think my logic is okay in printing the list with the indices but no input is coming out :(

At one point in fooling around with this, I was still unable to print the list of nodes but the "enter in the index you wish to delete" was output and was able to take a users' selection but eventually got a NullPointerException.

            else if (menu.equals("d")) {
            EntryNode temp = head;
            while (temp != null) {
                for (int i = 0; i < addressBook.length(); i++) {
                    //gets node at index
                    System.out.println(temp.getFirstName() + i);
                    temp = temp.getNext();
                }
            System.out.println(" ");
            System.out.println("Please enter the index of the entry you wish to delete ");
            int index = keyboard.nextInt();
            addressBook.removeEntry(index);
            }

        }

The removal method: public void removeEntry(int index){

    //delete from the head
    if (index == 0) {
        EntryNode temp = head;
        head = temp.getNext();
        temp.setNext(null);
        head.setPrev(null);
        size--;
    }
    //delete from the tail
    else if (index == length()) {
        EntryNode temp = tail;
        temp.setPrev(null);
        tail.setNext(null);
        tail = temp.getPrev();

        size--;
    }
    //in the middle
    else {
        EntryNode temp = head;
        for (int i = 0; i < index; i++) {
            //gets node at index
            temp = temp.getNext();
        }
        //set node after temp's previous to temp's previous 
        temp.getNext().setPrev(temp.getPrev());
        temp.getPrev().setNext(temp.getNext());
        temp.setNext(null);
        temp.setPrev(null);
        size--;
    }
}

The NullPointerException comes from :

//set node after temp's previous to temp's previous 
temp.getNext().setPrev(temp.getPrev());

Shouldn't else if (index == length()) { be else if (index == length() -1 ) { instead? If you start indexing from 0 and length() is the number of elements, the index of the tail will be length() - 1 and not length(). — biziclop
– biziclop, Commented Mar 9, 2012 at 15:39

Sapan Diwakar · Accepted Answer · 2012-03-09 15:39:19Z

2

You should check if temp.getNext() is not null before calling the setPrev() on it.

Also, you should check with length()-1 as you have nodes which are zero indexed.

answered Mar 9, 2012 at 15:39

Sapan Diwakar

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13 Comments

jackie Over a year ago

If temp.getNext() is null, isn't temp tail then?

biziclop Over a year ago

Yes, but if you do your null checks properly, you won't have to have a special case for head and tail.

Sapan Diwakar Over a year ago

@JackieAldama Yes. Its going to in the middle block because your length is probably not correct (Is it returning actual-length (then modify your condition) or actual-length - 1?).

jackie Over a year ago

Okay I updated this to if, else statement to check if temp==head, temp.getNext() == null, or else...

jackie Over a year ago

Regarding the first part of the question though, is there something clearly wrong with the way I am trying to output the list with indices for user input?

|

Alexander Pavlov · Accepted Answer · 2012-03-09 15:38:22Z

1

Indices are in the range [0, length() - 1], so you should use

else if (index == length() - 1) {

instead.

answered Mar 9, 2012 at 15:38

Alexander Pavlov

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