编写一个简单的PHP操作提示类

<?php
class Tips{
	private $tips;
	static private $_instance;
	
	private function __construct($string, $url)
	{
		$this->tips = "
<meta http-equiv=refresh content=4;url=$url>
<div style='border:1px solid #B4D8F4; width:320px; height:120px; margin:0 auto; font-size:12px;'>
	<div style='background-color:#CDE6F9; height:20px;'></div>
	<div align='center' style='font-size:14px; font-weight:bold; margin:20px 0 20px 0;'>$string</div>
	<div align='center'><a href='$url'>返回</a> （4秒后自动返回）</div>
</div>
	";
		return $this->tips;
	}
	public function __toString(){
        return $this->tips;
    }
	
	private function __clone(){}
	
	public static function get_tips($string, $url)
	{
		
		if( FALSE == (self::$_instance instanceof self) )
		{
			self::$_instance = new self($string, $url);
		}
		return self::$_instance;
    }
}
?>

	include_once("./tips_class.php");
	$hit = "错误：两次输入的密码不一致";
	$jump = "../login.php";
	echo $tips = Tips::get_tips($hit, $jump);