PHP设计模式之：单例模式

 1 <?php
 2 
 3 //单例模式
 4 class Database{
 5     private $_db;
 6     public static $_instance;
 7 
 8     //private的构造函数，防止被实例化
 9     private function __construct(){
10         $this->__db = pg_connect('dbname=test');
11     }
12 
13     public static function getInstance(){
14         if(!(self::$_instance instanceof self)){
15             self::$_instance = new self();
16         }
17         return self::$_instance;
18     }
19 
20     //private的clone方法，防止对象clone后产生多个实例对象
21     private function __clone(){
22         trigger_error('Clone is not allow' ,E_USER_ERROR);
23     }
24 
25     public function query($sql){
26         return pg_query($this->$_db,$sql);
27     }
28 }
29 
30 //调用方法
31 $conn = Database::getInstance();
32 $conn->query(' select * from user ');