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php使用类继承解决代码重复的问题,php代码
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php使用类继承解决代码重复的问题,php代码

Jun 13, 2016 am 09:14 AM
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php使用类继承解决代码重复的问题,php代码

本文实例讲述了php使用类继承解决代码重复的问题。分享给大家供大家参考。具体分析如下:

继承直白地说就是给一个类建一个或多个子类,要创建子类就必须在类声明中使用 extends 关键字,新类名在前,extends 在中,父类名在后。
 
下例中,我们创建两个新类,BookProduct 和Cdproduct ,它们都继承自 ShopProduct 类。

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 $numPages;   // 声明属性
 public $playLenth;
 public $title;
 public $producerMainName;
 public $producerFirstName;
 public $price;
 function __construct($title,$firstName,$mainName,$price,$numPages=0,$playLenth=0){
  $this -> title = $title;    // 给属性 title 赋传进来的值
  $this -> producerFirstName= $firstName;
  $this -> producerMainName = $mainName;
  $this -> price= $price;
  $this -> numPages= $numPages;
  $this -> playLenth= $playLenth;
 }
 function getProducer(){    // 声明方法
  return "{$this -> producerFirstName }"."{$this -> producerMainName}";
 }
 function getSummaryLine(){
  $base = "{$this->title}( {$this->producerMainName},";
  $base .= "{$this->producerFirstName} )";
  return $base;
 }
}

class CdProduct extends ShopProduct {
 function getPlayLength(){
  return $this -> playLength;
 }
 function getSummaryLine(){
  $base = "{$this->title}( {$this->producerMainName},";
  $base .= "{$this->producerFirstName} )";
  $base .= ":playing time - {$this->playLength} )";
  return $base;
 }
}

class BookProduct extends ShopProduct {
 function getNumberOfPages(){
  return $this -> numPages;
 }
 function getSummaryLine(){
  $base = "{$this->title}( {$this->producerMainName},";
  $base .= "{$this->producerFirstName} )";
  $base .= ":page cont - {$this->numPages} )";
  return $base;
 }
}
?>


 
由于子类没有定义构造方法,所以在实例化 BookProduct 和Cdproduct 类时,会自动调用父类 ShopProduct 的构造方法。

子类默认继承了父类所有的 public 和 protected方法与属性(但没有继承 private 方法与属性,后面会讲到这三个关键字的作用)。也就是说,我们可以在从 Cdproduct 类实例化的对象中调用 getProducer() 方法,尽管 getProducer() 是在 ShopProduct 类中定义的。
 
将一下代码加到上面:

复制代码 代码如下:

$product2 = new CdProduct("PHP面向对象","郭","碗瓢盆",7,null,"7小时");
print "美好生活:{$product2 -> getProducer()}
";
// 结果是:美好生活:郭碗瓢盆

这两个子类都继承了父类的公共部分,但注意, BookProduct 和Cdproduct 类都覆写了 getSummaryLine() 方法,提供了自己独特的实现,说明子类可以拓展和修改父类的功能。

但该方法在父类中的实现似乎有点多余,因为它的两个子类都重写了该方法,不过其他子类可能会用到它的基本功能。该方法的存在为客户端代码提供了保证:所有的 ShopProduct 对象都将有 getSummaryLine() 方法, BookProduct 和Cdproduct 都使用各自的 getSummaryLine() 方法访问 $title 属性。
 
可能一开始,继承是一个不太容易理解的概念。首先我们可以知道,通过定义一个从其他类继承而来的类,我们确保一个类拥有其自由的功能和父类的功能。然后就是子类的“搜索”功能,当我们调用 $product2 -> getProducer() 时,在 CdProduct 类中并没有找到 getProducer() 方法,那么就查找 ShopProduct 类中是否有这个方法,有就调用,没有则报错。对属性的访问也是同样的道理。
 
看看 ShopProduct 的构造方法,就会发现我们仍然在 基类(父类)中管理本应是子类处理的数据:BookProduct 应该处理 $numPages 参数和属性;Cdproduct 应该处理 $playLength 参数和属性。要完成这个工作,我们需要在子类中分别定义构造方法。

希望本文所述对大家的php程序设计有所帮助。

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