How does & bit operator work here?

In Java Collection classes, I have noticed very often codes like below

  //ArrayDeque
    public E pollFirst() {
    int h = head;
    @SuppressWarnings("unchecked")
    E result = (E) elements[h];
    // Element is null if deque empty
    if (result == null)
        return null;
    elements[h] = null;     // Must null out slot
    head = (h + 1) & (elements.length - 1);
    return result;
}

What does head = (h + 1) & (elements.length - 1); do ? Why is & operator used here and what purpose does it serve.

My Question is not how & works, but what's its use here.

Can anyone explain it ?