//inv : size >= 0
public class ArrayQueueModule {


	private final static int MAX_SIZE = 6;
	private static Object[] elements = new Object[MAX_SIZE];
	private static int head = 0;
	private static int tail = -1;
	private static int size = 0;

	//pre: size > 0
	//post: return first element in queue
	  public static Object element() {
	        assert size() > 0;

	        return elements[head];
	    }

	//pre: size > 0
	//post: return first element in queue, remove it from queue
	public static Object dequeue() {
		assert size > 0;
		size --;
		return elements[(head++) % elements.length];
	}

	//pre: true
	//post: return size == 0
	public static boolean isEmpty() {
		return size == 0;
	}

	//pre: true
	//post: return count of elements in queue
	public static int size() {
		return size;
	}

	//pre: true
	//post: element() = e
	public static void enqueue(java.lang.Object e) {
		ensureCapasity(size + 1);
		size++;
		elements[++tail % elements.length] = e;
	}

	//pre: true
	//post: size == 0
	public static void clear() {
		size = 0;
		head = 0;
		tail = -1;
		elements = null;
		elements = new Object[MAX_SIZE];
	}


	//pre: capasity = size
	//post: if (capasity > elements.length) elements.length = 2 * elements.length
	private static void ensureCapasity(int capacity) {
		if (capacity <= elements.length) {
			return;
		}
		Object[] temp = new Object[2 * elements.length];
		for (int i = head; i < head + size; i++) {
			temp[i - head] = elements[i % elements.length];
		}

		elements = null;
		elements = temp;
		temp = null;
		head = 0;
		tail = size - 1;
	}
}