删除链表中的节点

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());

Answer 1

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.

Answer 2

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

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

instead.