随缘

class MySQL {
	private $dbhost = 'localhost';
	private $dbuser = 'root';
	private $dbpass = '123';
	private $db	    = 'test';
 
	public $guid;
 
	//======================================
	// 函数: connect()
	// 功能: 连接数据库
	// 返回:
	//======================================
	public function __construct()
	{
		$this->link_id = mysql_connect($this->dbhost, $this->dbuser, $this->dbpass);
		$this->guid = md5(uniqid());
		if (!$this->link_id)
		{
			$this->halt("数据库连接失败.请检查连接参数.");
			return;
		}
 
		if (!mysql_select_db($this->db, $this->link_id))
		{
			$this->halt("选择数据库".$this->db."失败.");
			return;
		}
		mysql_query("SET NAMES 'utf8'");
	}
}

<?php
class Singleton {
	private $_db;
	private static $_single = null;
 
	public static function getInstance() {
		if (self::$_single === null)
			self::$_single = new Singleton();
		return self::$_single;
	}
 
	function __construct() {
		$this->_db = new MySQL();
	}
 
	public function db() {
		return $this->_db;
	}
}
 
/* End of file */
/* Location: */

<?PHP
require_once ('MySQL.php');
require_once ('Singleton.php');
header('content-type:text/html; charset=utf-8');
 
echo '单件模式____________________________<br />';
$s1 = Singleton::getInstance()->db();
$s2 = Singleton::getInstance()->db();
echo '$s1->guid:'.$s1->guid.'<br />';
echo '$s1->guid:'.$s2->guid.'<br />';
echo ($s1 === $s2) ? 'true' : 'false';
echo '<br />';
 
echo '直接实例化对象________________________________<br />';
$d1 = new MySQL();
echo '$d->guid:'.$d1->guid.'<br />';
$d2 = new MySQL();
echo '$d1->guid:'.$d2->guid.'<br />';
echo ($d1 === $d2) ? 'true' : 'false';
?>