PHP 类 方法 class function extends

<?php
class SiteInfo { 
    var $url;

    function __construct($para) {
        $this->url = $para;
    }

    function setUrl($para){
        $this->url = $para;
    }

    function getUrl(){
        echo $this->url;
    }
}

$my = new SiteInfo("https://chanpinxue.cn");
$my->getUrl();
?>

<?php
class SiteInfoBoy extends SiteInfo { 
    var $url;

    function __construct($para) {
        $this->url = $para;
    }

    function setUrl($para){
        $this->url = $para;
    }

    function getUrl(){
    // 调用父类中被覆盖的方法
        parent::getUrl();

        echo ' website:'. $this->url;
    }
}

$me = new SiteInfoBoy("http://chanpinxue.cn");
$me->getUrl();
?>