public class SequenceStack {
	private String[] urls; // 数组，存储用户请求的url
	private int top; // 栈顶指针
	private final static int maxSize = 20; // 数组长度

	public SequenceStack() {
		urls = new String[maxSize];
		top = -1;
	}

	// url入栈
	public void push(String url) {
		if (top == maxSize - 1) { // 栈满处理
			if (url.equals(urls[top])) {// 防止刷新，如果栈顶url与传入的url相等，即为刷新操作
				return;
			}
			// 更新数组保存的url
			String[] otherUrls = urls.clone();
			for (int i = 0; i <= maxSize - 1; i++) {
				if (i == top) {
					break;
				}
				otherUrls[i] = urls[i + 1];// 前移
			}
			otherUrls[top] = url;
			urls = otherUrls;
		} else { // 栈未满
			top++;
			urls[top] = url;
		}
	}

	// 栈顶元素即为前页的url
	public String pop() {
		if (top == -1 || top == 0) {
			return null;
		}
		return urls[top];
	}

	public String[] getUrls() {
		return urls;
	}

	public void setUrls(String[] urls) {
		this.urls = urls;
	}

	public int getTop() {
		return top;
	}

	public void setTop(int top) {
		this.top = top;
	}

	public static int getMaxsize() {
		return maxSize;
	}
}