17php模版模式

<?php abstract class sale{
    public $price = 0;
    
    public final function setprice(){
        $this->price += $this->Tax();
        $this->price -= $this->sale();
    }
    
    //税务
    protected function Tax(){
        return 0;
    }
    
    //租金
    protected abstract function sale(); 
}

class Book extends sale{
    public $name;
    public $author;
    
    function __construct($name, $author, $price){
        $this->name = $name;
        $this->author = $author;
        $this->price = $price;
    }
    
    function sale(){
        return $this->price*0.1;
    }
}

$book = new Book('《夜航西飞》', "马卡姆 柏瑞尔",100);
$book->setprice();
echo $book->price;