php实现parent调用父类的构造方法与被覆写的方法,parent被覆
本文实例讲述了php实现parent调用父类的构造方法与被覆写的方法。分享给大家供大家参考。具体分析如下:
覆写:被重新设计。
在子类中定义构造方法时,需要传递参数给父类的构造方法,否则我们得到的可能是一个构造不完整的对象。
要调用父类的方法,首先要找到一个引用类本身的途径:句柄(handle),PHP为此提供了parent关键字。
parent 调用父类的构造方法
要引用一个类而不是对象的方法,可以使用 ::(两个冒号),而不是 ->。
所以, parent::__construct() 以为着调用父类的 __construct() 方法。
修改上篇《使用类继承解决代码重复等问题》中的代码,让每个类只处理自己的数据:
复制代码 代码如下:
header('Content-type:text/html;charset=utf-8');
// 从这篇开始,类名首字母一律大写,规范写法
class ShopProduct{ // 声明类
public $title; // 声明属性
public $producerMainName;
public $producerFirstName;
public $price;
function __construct($title,$firstName,$mainName,$price){
$this -> title = $title; // 给属性 title 赋传进来的值
$this -> producerFirstName= $firstName;
$this -> producerMainName = $mainName;
$this -> price= $price;
}
function getProducer(){ // 声明方法
return "{$this -> producerFirstName }"."{$this -> producerMainName}";
}
function getSummaryLine(){
$base = "{$this->title}( {$this->producerMainName},";
$base .= "{$this->producerFirstName} )";
return $base;
}
}
class CdProduct extends ShopProduct {
public $playLenth;
function __construct($title,$firstName,$mainName,$price,$playLenth){
parent::__construct($title,$firstName,$mainName,$price);
$this -> playLenth= $playLenth;
}
function getPlayLength(){
return $this -> playLength;
}
function getSummaryLine(){
$base = "{$this->title}( {$this->producerMainName},";
$base .= "{$this->producerFirstName} )";
$base .= ":playing time - {$this->playLength} )";
return $base;
}
}
// 定义类
class BookProduct extends ShopProduct {
public $numPages;
function __construct($title,$firstName,$mainName,$price,$numPages){
parent::__construct($title,$firstName,$mainName,$price);
$this -> numPages= $numPages;
}
function getNumberOfPages(){
return $this -> numPages;
}
function getSummaryLine(){
$base = "{$this->title}( {$this->producerMainName},";
$base .= "{$this->producerFirstName} )";
$base .= ":page cont - {$this->numPages} )";
return $base;
}
}
?>
每个子类都会在设置自己的属性前调用父类的构造方法。基类(父类)现在仅知道自己的数据,而我们也应该尽量避免告诉父类任何关于子类的信息,这是一条经验规则,大家想想如果某个子类的信息应该是”保密“的,结果父类知道它的信息,其它子类可以继承,这样子类的信息就不保密了。
parent 调用父类被覆写的方法
parent 关键字可以在任何覆写父类的方法中使用。覆写一个父类的方法时,我们并不希望删除父类的功能,而是拓展它,通过在当前对象中调用父类的方法可以达到这个目的。
看看上面的代码,可以发现两个子类中 getSummaryLine() 方法中重复了许多代码,我们应该利用 ShopProduct 类中已经存在的功能,而不是重复开发:
复制代码 代码如下:
// 父类:ShopProduct
function getSummaryLine(){
$base = "{$this->title}( {$this->producerMainName},";
$base .= "{$this->producerFirstName} )";
return $base;
}
// 子类:CdProduct
function getSummaryLine(){
$base = parent::getSummaryLine();
$base .= ":playing time - {$this->playLength} )";
return $base;
}
// 子类:BookProduct
function getSummaryLine(){
$base = parent::getSummaryLine();
$base .= ":page cont - {$this->numPages} )";
return $base;
}
我们在父类 ShopProduct 中为 getSummaryLine() 方法完成了”核心“功能,接着在子类中简单的调用父类的方法,然后增加更多数据到摘要字符串,方法的拓展就实现了。
希望本文所述对大家的php程序设计有所帮助。

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