php多态

<?php
#多态
abstract class tiger{
public abstract function climb();
}

class xtiger extends tiger{
public function climb(){
echo "摔下来;";
}
}

class mtiger extends tiger{
public function climb(){
echo "爬到树顶;";
}
}

class cat {
public function climb(){
echo "飞到天上";
}
}

class client{
public static function call(tiger $animal){
$animal->climb();
}
}
client::call(new xtiger());
client::call(new mtiger());
client::call(new cat());#Catchable fatal error