Priority Queue Linked List Iterator NPE

Asked Jul 31 '16 at 17:12

Active Jul 31 '16 at 17:21

Viewed 16 times

Just like the title says, I am getting a null pointer exception whenever I try to call the iterator from my driver. The error points to this specific location in my class:

 public Iterator<E> iterator() {
    return new IteratorHelper();
}

    class IteratorHelper implements Iterator<E> {
    private int iteratorIndex;
    private long modCheck;
    Node<E> current;

    public IteratorHelper() {

        iteratorIndex = 0;
        modCheck = sequenceNumber;
        current = head;
    }

    public boolean hasNext() {
        if (modCheck != sequenceNumber)
            throw new ConcurrentModificationException();
        return iteratorIndex < currentSize;
    }

    public E next() {
        if (!hasNext() && current != null)
            throw new NoSuchElementException();
        iteratorIndex++;
        current = current.next;
        return current.data; //NPE <<<<<<<<<<
    }

    public void remove() {
        throw new UnsupportedOperationException();
    }
}

}

Why am I getting a NPE?

edited Jul 31 '16 at 17:21

asked Jul 31 '16 at 17:12

Orcka

what is current initialized to? What if you have last node as current pointing to null, what do you think current.data would return then? – SMA Jul 31 '16 at 17:14
2

Short answer: because something is `null`. Please refer to the linked question. – Tunaki Jul 31 '16 at 17:14
We need to see more of the code, if the class is not initialized properly the you wouldnt be able to even call #next() without the NPE.... – ΦXocę 웃 Пepeúpa ツ Jul 31 '16 at 17:14
Probably `current` is null. try with `if (current == null || !hasNext())` – David Pérez Cabrera Jul 31 '16 at 17:14
The error points to *what* specific location in your class? – user207421 Jul 31 '16 at 17:16
I updated the question with the whole iterator. – Orcka Jul 31 '16 at 17:18

Priority Queue Linked List Iterator NPE

0 Answers0