';    }}class MTiger extends Tiger{    public function climb(){        echo '爬到树顶
';    }}/*调用类*/class Client{    public static function call($animal){        $animal->climb();    }}Client::call(new XTiger()); //输出：“摔下来”Client::call(new MTiger()); //输出：“爬到树顶”//----------------------------------------------------class Cat{    public function climb(){        echo '飞到天上';    }}Client::call(new Cat()); //输出：“飞到天上”