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