单例模式
当需要保证某个对象只能有一个实例的时候，单例模式非常有用。它把创建对象的控制权委托到一个单一的点上，任何时候应用程序都只会仅有一个实例存在。
单例模式中必须包含：private 的构造函数、静态变量、公共静态方法、private clone方法。
下面举个栗子
<?php/** mysql 单例*/class mysql{ ???private $host ???=‘yourhost‘; //数据库主机 ???private $user ????= ‘youruser‘; //数据库用户名 ???private $pwd ????= ‘yourpwd‘; //数据库用户名密码 ???private $database = ‘database‘; //数据库名 ???private $charset = ‘utf8‘; //数据库编码，GBK,UTF8,gb2312 ???private $link; ????????????//数据库连接标识; ???private $rows; ????????????//查询获取的多行数组 ???static $_instance; //存储对象 ???/** ????* 私有构造函数 ????*/ ???private function __construct($pconnect = false) { ???????if (!$pconnect) { ???????????$this->link = @ mysql_connect($this->host, $this->user, $this->pwd) or $this->err(); ???????} else { ???????????$this->link = @ mysql_pconnect($this->host, $this->user, $this->pwd) or $this->err(); ???????} ???????mysql_select_db($this->database) or $this->err(); ???????$this->query("SET NAMES ‘{$this->charset}‘", $this->link); ???????return $this->link; ???} ???/** ????* 防止被克隆 ????* ????*/ ???private function __clone(){} ???public static function getInstance($pconnect = false){ ???????if(FALSE == (self::$_instance instanceof self)){ ???????????self::$_instance = new self($pconnect); ???????} ???????return self::$_instance; ???} ???/** ????* 查询 ????*/ ???public function query($sql, $link = ‘‘) { ???????$this->result = mysql_query($sql, $this->link) or $this->err($sql); ???????return $this->result; ???} ???/** ????* 单行记录 ????*/ ???public function getRow($sql, $type = MYSQL_ASSOC) { ???????$result = $this->query($sql); ???????return @ mysql_fetch_array($result, $type); ???} ???/** ????* 多行记录 ????*/ ???public function getRows($sql, $type = MYSQL_ASSOC) { ???????$result = $this->query($sql); ???????while ($row = @ mysql_fetch_array($result, $type)) { ???????????$this->rows[] = $row; ???????} ???????return $this->rows; ???} ???/** ????* 错误信息输出 ????*/ ???protected function err($sql = null) { ???????????}}//用例$db = mysql::getInstance();$db2 = mysql::getInstance();$data = $db->getRows(‘select * from blog‘);//print_r($data);//判断两个对象是否相等if($db === $db2){ ???echo ‘true‘;}?>php 单例模式
原文地址：https://www.cnblogs.com/pfdltutu/p/9019194.html