(转)PHP 单例模式

 1 <?php 2  3 /* 单例模式举例,其要点如下: 4  * 5  * 1. $_instance 必须声明为静态的私有变量 6  * 2. 构造函数和克隆函数必须声明为私有的,这是为了防止外部程序 new 类从而失去单例模式的意义 7  * 3. getInstance()方法必须声明为公有的,必须调用此方法以返回唯一实例的一个引用 8  * 4. ::操作符只能访问静态变量或静态函数 9  *10  */11 12 class People {13     private static $_instance = NULL;14 15     public $height = '';16 17     public $age = '';18 19     private function __construct() {20         $this -> height = '185';21         $this -> age = 25;22     }23 24     private function __clone() {25         //do something26     }27 28     static public function getInstance() {29         if (!self::$_instance instanceof self) {30             //echo 'lgh-big';31             self::$_instance = new self();32         } else {33             //for testing only34             //echo 'gdc-xiaoairener';35         }36 37         return self::$_instance;38     }39 40     public function getHeight() {41         echo $this -> height;42     }43 44     public function getAge() {45         echo $this -> age;46     }47 48 }49 50 function testInstance() {51     People::getInstance() -> getAge();52 }53 54 //begin to use the class55 56 $lgh = People::getInstance();57 $lgh -> getHeight();58 59 echo '<br />';60 testInstance();61 ?>