ArrayQueueModule

public class ArrayQueueModule {
    private static int head;
    private static int tail;
    private static Object[] queue = new Object[5];

    public static int size() {
        if (head > tail) {
            return queue.length - head + tail;
        } else {
            return tail - head;
        }
    }

    public static void enqueue(Object element) {
        assert element != null;

        ensureCapacity(size() + 1);
        queue[tail] = element;
        tail = (tail + 1) % queue.length;
    }

    private static void ensureCapacity(int capacity) {
        if (capacity <= queue.length) {
            return;
        }

        Object[] newQueue = new Object[2 * capacity];
        for (int i = 0; i < size(); i++) {
            newQueue[i] = queue[i];
        }
        queue = newQueue;
    }

    public static Object element() {
        assert size() > 0;

        return queue[head];
    }

    public static Object dequeue() {
        assert size() > 0;

        Object x = queue[head];
        head = (head + 1) % queue.length;
        return x;
    }

    public static boolean isEmpty() {
        return head == tail;
    }

    public static void clear() {
        head = 0;
        tail = 0;
    }
}