Php面向对象 抽象类
Php面向对象 -- 抽象类
抽象类abstract:
有一种类,只能被继承,不能实例化对象。原因就是这个类的定义不完整。
因为php支持定义一种,只有方法的声明部分,而没有方法的实现部分的不完整方法。
如果某个类,包含了这种不完整的方法,就不是不完整类,也就不能实例化对象。
不完整的类,称之抽象类
所包含的不完整的方法,称之抽象方法。
定义:
包含抽象方法的类,就是抽象类。
语法:
定义抽象方法,利用abstract的关键字,告知php那个方法为抽象方法
如果一个类包含一个抽象方法,也就是抽象类,因此也需要使用abstract关键字声明
例子:
abstract class Goods
{
public $goods_name;
public $shop_price;
public function __construct($name,$price)
{
$this->goods_name= $name;
$this->shop_price= $price;
}
//抽象方法
abstract public function sayName();
}
class GoodsBook extends Goods
{
public $pages;
public function __construct($name,$price,$pages)
{
parent::__construct($name,$price);
$this->pages= $pages;
}
// 继承抽象类的子类要实现抽象类中的 抽象方法
public function sayName()
{
echo$this->goods_name;
}
}
抽象类没有实例化对象的能力,只有被继承的能力。
如果继承某个抽象类的类是非抽象类的话,就一定要将不完整的抽象方法实现,否则该类也应该是一个抽象类。
注:子类中实现抽象类的抽象方法时,方法名、参数要一致,访问权限要弱于抽象类的访问权限。
例子:
abstruct class Goods
{
abstruct protected function sayName();
}
class GoodsBook extends Goods
{
public function sayName()
{
}
}
抽象类功能总结:
在可以为子类提供公共操作的同时,限制子类所用有得方法的结构。
牺牲了实例化对象的功能。

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