Infinite loop because the iterator doesn't move

Question

There is a some class which implementing an interface Selector . I should use iterator() in its methods.

private class SequenceSelector implements Selector {
    private T obj = items.iterator().next();
    public boolean end() { return !items.iterator().hasNext(); }
    public T current() { return obj; }
    public void next() { obj = items.iterator().next(); }
}

items is a ArrayList. obj is a value in order to save the first sequence member before the first next() using.

With a following code the program goes into an infinite loop in which is printed only the first member of sequence.

while(!selector.end()) {
      System.out.print(selector.current() + " ");
      selector.next();
}

Why does this happens? Though I use next() method, the iterator doesn't move.

Answer 1

Every time you call items.iterator() you create a new iterator.

Create one iterator at the start, and use that repeatedly.

private class SequenceSelector implements Selector {
    private final Iterator<T> iterator = items.iterator();

    private T obj = iterator.next();
    public boolean end() { return !iterator.hasNext(); }
    public T current() { return obj; }
    public void next() { obj = iterator.next(); }
}