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)

int110

string'SINGLEB CHANGED: ' (length=17)

int-400