public static void main(String[] args) {
        Stack<String> stack = new Stack<String>();
        stack.push("zhu");
        stack.push("zhen");
        stack.push("guang");

        for (String s : stack) {
            StdOut.println(s);
        }

        StdOut.println("======================");

        StdOut.println(stack.pop());

        StdOut.println("======================");

        for (String s : stack) {
            StdOut.println(s);
        }

        Iterator<String> it = stack.iterator();
        while (it.hasNext())
            it.remove();
        System.out.println(stack.size());
    }