PHP计算程序运行时间的类

<?php
class runTime{
private $starTime;
private $stopTime;
private function getMicTime(){
$mictime=microtime(true);
list($usec,$sec)=explode(' ',$mictime);
return (float)$usec+(float)$sec;
}

public function star(){
$this->starTime=$this->getMicTime();
}

public function stop(){
$this->stopTime=$this->getMicTime();
}

public function spent(){
return round($this->stopTime-$this->starTime)*1000;//单位：毫秒数
}
}

//类使用方法介绍
$time=new runTime();
$time->star();//该语句尽量写在代码段的最开始处

//程序代码段

$time->stop();//该语句最好写在代码段的最结尾处
echo $time->spent();