dequeue()

/* Removes an item from the front of the queue, and returns its data */
public Item dequeue() {
    Item item = q[head];                            // 1
    q[head] = null;                                 // 2
    head = (head + 1) % q.length;                   // 3

    if (length > 0 && length == q.length / 4) {     // 4
        resize(q.length / 2);                       // 4
    }                                               // 4

    length--;                                       // 5
    return item;                                    // 6
}