PHP里的单例类写法实例

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;  }}

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();  }}

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();  }}

$instA = new SINGLEA();$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());

string'SINGLEA CHANGED: ' (length=17)int110string'SINGLEB CHANGED: ' (length=17)int-400