单例模式--实例讲解

class Preferences {
private $props = array();
private static $instance;

private   function __construct(){}

public static function getInstance(){
if(empty(self::$instance)){
self::$instance = new Preferences();
}
return self::$instance;
}

public function setProperty($key,$value){
$this->props[$key] = $value;
}

public function getProperty($key){
return $this->props[$key];
}
}

$pref = Preferences::getInstance();
$pref->setProperty('name','captain');
var_dump($pref);
echo $pref->getProperty('name')."<br>"; //输出:captain

unset($pref);
$pref2 = Preferences::getInstance();
var_dump($pref2);
echo $pref2->getProperty('name');   //输出captain