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<?php
class?Car?{
????public?$speed?=?0;?//汽車的起始速度是0
????
????public?function?speedUp()?{
????????$this->speed?+=?10;
????????return?$this->speed;
????}
}
//定義繼承于Car的Truck類
class?Truck?extends?Car{
????public?function?speedUp(){
????????$this->speed=parent::speedUp()+40;
????}
}

$car?=?new?Truck();
$car->speedUp();
echo?$car->speed;

這樣可以了