php里的单实例类在进行数据交换，节省内存上还是很有意义的。写个简单例子。
类1，单实例类本身：
class util { private static $instance; public function get() { if (!self::$instance) { self::$instance = new util(); } return self::$instance; } public $number = 10; public function change($num) { $this->number += $num; } public function getnum() { return $this->number; }}
类2，使用前述单实例类的应用类：
class singlea { private $numinst; function __construct() { $this->numinst = util::get(); } public function change($num) { $this->numinst->change($num); } public function getnum() { return $this->numinst->getnum(); }}
类3，同类2：
class singleb { private $numinst; function __construct() { $this->numinst = util::get(); } public function change($num) { $this->numinst->change($num); } public function getnum() { return $this->numinst->getnum(); }}
最后是调用的地方：
$insta = new singlea();$insta->change(100);var_dump('singlea changed: ');var_dump($insta->getnum());$instb = new singleb();$instb->change(-510);var_dump('singleb changed: ');var_dump($instb->getnum());
最后的显示结果：
string'singlea changed: ' (length=17)int110string'singleb changed: ' (length=17)int-400