java用数组实现队列，可以rebuild

public class ArrayQueue {
	private String[] items;
	private int n;
	private int head;
	private int tail;

	public ArrayQueue(int n) {
		this.n = n;
		items = new String[n];
		head = tail = 0;
	}

	public String out() {
		if (head == n - 1) {
			String item = items[head];
			head = tail = 0;
			return item;
		} else if (head == tail) {
			return null;
		} else {
			return items[head++];
		}
	}

	public boolean in(String item) {
		if (tail <= n - 1) {
			items[tail++] = item;
			return true;
		}
		if (head == 0) {
			return false;
		}
		rebuild();
		items[tail++] = item;
		return true;
	}

	private void rebuild() {
		int index = head;
		for (int i = 0; i < tail - head; ++i) {
			items[i] = items[index++];
		}
		tail = tail - head;
		head = 0;
	}

	public static void main(String[] args) {
		ArrayQueue arrayQueue = new ArrayQueue(6);
		System.out.println(arrayQueue.out());
		arrayQueue.in("qyd");
		arrayQueue.in("qyj");
		arrayQueue.in("qgl");
		arrayQueue.in("qyx");
		arrayQueue.in("hcy");
		arrayQueue.in("qfl");
		System.out.println(arrayQueue.in("xxx"));
		System.out.println(arrayQueue.out());
		arrayQueue.in("xxx");
		System.out.println(arrayQueue.out());
		System.out.println(arrayQueue.out());
		System.out.println(arrayQueue.out());
		System.out.println(arrayQueue.out());
		System.out.println(arrayQueue.out());
		System.out.println(arrayQueue.out());
		System.out.println(arrayQueue.out());
	}
}