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 

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 ');