PHP面向对象继承用法详解(优化与减少代码重复)

本文实例讲述了PHP面向对象继承用法。分享给大家供大家参考，具体如下：

继承

先看两个类

<?php
class CdProduct {
 public $playLength; // 播放时间
 public $title;
 public $producerMainName;
 public $producerFirstName;
 public $price;
 function __construct(  $title, $firstName,
             $mainName, $price,
             $playLength ) {
   $this->title       = $title;
   $this->producerFirstName = $firstName;
   $this->producerMainName = $mainName;
   $this->price       = $price;
   $this->playLength    = $playLength;
 }
 function getPlayLength() {
   return $this->playLength;
 }
 function getSummaryLine() {
   $base = "{$this->title} ( {$this->producerMainName}, ";
   $base .= "{$this->producerFirstName} )";
   $base .= ": playing time - {$this->playLength}";
   return $base;
 }
 function getProducer() {
   return "{$this->producerFirstName}".
       " {$this->producerMainName}";
 }
}
class BookProduct {
 public $numPages; // 看的页数
 public $title;
 public $producerMainName;
 public $producerFirstName;
 public $price;
 function __construct(  $title, $firstName,
             $mainName, $price,
             $numPages ) {
   $this->title       = $title;
   $this->producerFirstName = $firstName;
   $this->producerMainName = $mainName;
   $this->price       = $price;
   $this->numPages     = $numPages;
 }
 function getNumberOfPages() {
   return $this->numPages;
 }
 function getSummaryLine() {
   $base = "{$this->title} ( {$this->producerMainName}, ";
   $base .= "{$this->producerFirstName} )";
   $base .= ": page count - {$this->numPages}";
   return $base;
 }
 function getProducer() {
   return "{$this->producerFirstName}".
       " {$this->producerMainName}";
 }
}
$product1 = new CdProduct("cd1", "bob", "bobbleson", 4, 50 );
print $product1->getSummaryLine();
print "\n";
$product2 = new BookProduct("book1", "harry", "harrelson", 4, 30 );
print $product2->getSummaryLine();
print "\n";
?>

输出：

cd1 ( bobbleson, bob ): playing time - 50
book1 ( harrelson, harry ): page count - 30

点评：这两个类，代码重复性太高，有相同性，也有差异性。不如用继承来简化处理。

采用继承来处理

<?php
class ShopProduct {
 public $numPages;
 public $playLength;
 public $title;
 public $producerMainName;
 public $producerFirstName;
 public $price;
 function __construct(  $title, $firstName,
             $mainName, $price,
             $numPages=0, $playLength=0 ) {
   $this->title       = $title;
   $this->producerFirstName = $firstName;
   $this->producerMainName = $mainName;
   $this->price       = $price;
   $this->numPages     = $numPages;
   $this->playLength    = $playLength;
 }
 function getProducer() {
   return "{$this->producerFirstName}".
       " {$this->producerMainName}";
 }
 function getSummaryLine() {
   $base = "$this->title ( {$this->producerMainName}, ";
   $base .= "{$this->producerFirstName} )";
   return $base;
 }
}
class CdProduct extends ShopProduct {
 function getPlayLength() { // 增加属于自己的方法
   return $this->playLength;
 }
 function getSummaryLine() { // 改造了父类的方法
   $base = "{$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} )";
   $base .= ": page count - {$this->numPages}";
   return $base;
 }
}
$product1 = new CdProduct("cd1", "bob", "bobbleson", 4, null, 50 );
print $product1->getSummaryLine();
print "\n";
$product2 = new BookProduct("book1", "harry", "harrelson", 4, 30 );
print $product2->getSummaryLine();
print "\n";
?>

输出：

cd1 ( bobbleson, bob ): playing time - 50
book1 ( harrelson, harry ): page count - 30

点评：继承处理很好的解决了差异性，相通性问题。

进一步优化处理

<?php
class ShopProduct {
 // 抽离出共有属性
 public $title;
 public $producerMainName;
 public $producerFirstName;
 public $price;
 function __construct(  $title, $firstName,
             $mainName, $price ) {
   $this->title       = $title;
   $this->producerFirstName = $firstName;
   $this->producerMainName = $mainName;
   $this->price       = $price;
 }
 function getProducer() {
   return "{$this->producerFirstName}".
       " {$this->producerMainName}";
 }
 function getSummaryLine() {
   $base = "{$this->title} ( {$this->producerMainName}, ";
   $base .= "{$this->producerFirstName} )";
   return $base;
 }
}
class CdProduct extends ShopProduct {
 // 抽离出属于自己特有的属性
 public $playLength;
 function __construct(  $title, $firstName,
             $mainName, $price, $playLength ) {
   parent::__construct(  $title, $firstName,
               $mainName, $price ); // 继承父类的构造函数
   $this->playLength = $playLength; // 处理自己专有的属性
 }
 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 {
 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 count - $this->numPages";
   return $base;
 }
}
$product1 = new CdProduct("cd1", "bob", "bobbleson", 4, 50 );
print $product1->getSummaryLine();
print "\n";
$product2 = new BookProduct("book1", "harry", "harrelson", 4, 30 );
print $product2->getSummaryLine();
print "\n";
?>

输出：

cd1 ( bobbleson, bob ): playing time - 50
book1 ( harrelson, harry ): page count - 30

点评：这里把共有属性在父类中，其他个性属性放在自己的类中处理。并设置自己的构造方法，继承父类的构造方法。

进一步继承父类的方法

<?php
class ShopProduct {
 public $title;
 public $producerMainName;
 public $producerFirstName;
 public $price;
 function __construct(  $title, $firstName,
             $mainName, $price ) {
   $this->title       = $title;
   $this->producerFirstName = $firstName;
   $this->producerMainName = $mainName;
   $this->price       = $price;
 }
 function getProducer() {
   return "{$this->producerFirstName}".
       " {$this->producerMainName}";
 }
 function getSummaryLine() {
   $base = "{$this->title} ( {$this->producerMainName}, ";
   $base .= "{$this->producerFirstName} )";
   return $base;
 }
}
class CdProduct extends ShopProduct {
 public $playLength;
 function __construct(  $title, $firstName,
             $mainName, $price, $playLength ) {
   parent::__construct(  $title, $firstName,
               $mainName, $price );
   $this->playLength = $playLength;
 }
 function getPlayLength() {
   return $this->playLength;
 }
 function getSummaryLine() {
   $base = parent::getSummaryLine();
   $base .= ": playing time - {$this->playLength}";
   return $base;
 }
}
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 = parent::getSummaryLine();
   $base .= ": page count - {$this->numPages}";
   return $base;
 }
}
$product1 = new CdProduct("cd1", "bob", "bobbleson", 4, 50 );
print $product1->getSummaryLine();
print "\n";
$product2 = new BookProduct("book1", "harry", "harrelson", 4, 30 );
print $product2->getSummaryLine();
print "\n";
?>

输出：

cd1 ( bobbleson, bob ): playing time - 50
book1 ( harrelson, harry ): page count - 30

点评：同样的结果，可以优化优化再优化。这里继承父类的方法。parent::getSummaryLine()。不过这个用的比较少。

继续添加一些有意思的内容

<?php
class ShopProduct {
 private $title;
 private $discount = 0;
 private $producerMainName;
 private $producerFirstName;
 protected $price;
 function __construct(  $title, $firstName,
             $mainName, $price ) {
   $this->title       = $title;
   $this->producerFirstName = $firstName;
   $this->producerMainName = $mainName;
   $this->price       = $price;
 }
 function setDiscount( $num ) {
   $this->discount=$num;
 }
 function getPrice() {
   return ($this->price - $this->discount);
 }
 function getProducer() {
   return "{$this->producerFirstName}".
       " {$this->producerMainName}";
 }
 function getSummaryLine() {
   $base = "{$this->title} ( {$this->producerMainName}, ";
   $base .= "{$this->producerFirstName} )";
   return $base;
 }
}
class CdProduct extends ShopProduct {
 public $playLength;
 function __construct(  $title, $firstName,
             $mainName, $price, $playLength ) {
   parent::__construct(  $title, $firstName,
               $mainName, $price );
   $this->playLength = $playLength;
 }
 function getPlayLength() {
   return $this->playLength;
 }
 function getSummaryLine() {
   $base = parent::getSummaryLine();
   $base .= ": playing time - {$this->playLength}";
   return $base;
 }
}
class BookProduct extends ShopProduct {
 public $numPages;
 function __construct(  $title, $firstName,
             $mainName, $price, $numPages ) {
   parent::__construct(  $title, $firstName,
               $mainName, $price );
   $this->numPages = $numPages;
 }
 function getPrice() {
   return $this->price;
 }
 function getNumberOfPages() {
   return $this->numPages;
 }
 function getSummaryLine() {
   $base = parent::getSummaryLine();
   $base .= ": page count - {$this->numPages}";
   return $base;
 }
}
$product1 = new CdProduct("cd1", "bob", "bobbleson", 4, 50 );
$product1->setDiscount( 3 );
print $product1->getSummaryLine();
print "\n";
print "price: {$product1->getPrice()}\n";
$product2 = new BookProduct("book1", "harry", "harrelson", 4, 30 );
$product2->setDiscount( 3 ); // 折扣对book无效
print $product2->getSummaryLine();
print "\n";
print "price: {$product2->getPrice()}\n";
?>

输出：

cd1 ( bobbleson, bob ): playing time - 50
price: 1
book1 ( harrelson, harry ): page count - 30
price: 4

点评:父类添加了折扣，book继承之后，修改了getPrice方法，所以折扣对book无效。

私有化属性，通过方法来设置与获取

<?php
class ShopProduct {
 // 私有化属性，通过方法来设置与获取
 private $title;
 private $producerMainName;
 private $producerFirstName;
 protected $price;
 private $discount = 0;
 public function __construct(  $title, $firstName,
             $mainName, $price ) {
   $this->title       = $title;
   $this->producerFirstName = $firstName;
   $this->producerMainName = $mainName;
   $this->price       = $price;
 }
 public function getProducerFirstName() {
   return $this->producerFirstName;
 }
 public function getProducerMainName() {
   return $this->producerMainName;
 }
 public function setDiscount( $num ) {
   $this->discount=$num;
 }
 public function getDiscount() {
   return $this->discount;
 }
 public function getTitle() {
   return $this->title;
 }
 public function getPrice() {
   return ($this->price - $this->discount);
 }
 public function getProducer() {
   return "{$this->producerFirstName}".
       " {$this->producerMainName}";
 }
 public function getSummaryLine() {
   $base = "{$this->title} ( {$this->producerMainName}, ";
   $base .= "{$this->producerFirstName} )";
   return $base;
 }
}
class CdProduct extends ShopProduct {
 private $playLength = 0;
 public function __construct(  $title, $firstName,
             $mainName, $price, $playLength ) {
   parent::__construct(  $title, $firstName,
               $mainName, $price );
   $this->playLength = $playLength;
 }
 public function getPlayLength() {
   return $this->playLength;
 }
 public function getSummaryLine() {
   $base = parent::getSummaryLine();
   $base .= ": playing time - {$this->playLength}";
   return $base;
 }
}
class BookProduct extends ShopProduct {
 private $numPages = 0;
 public function __construct(  $title, $firstName,
             $mainName, $price, $numPages ) {
   parent::__construct(  $title, $firstName,
               $mainName, $price );
   $this->numPages = $numPages;
 }
 public function getNumberOfPages() {
   return $this->numPages;
 }
 public function getSummaryLine() {
   $base = parent::getSummaryLine();
   $base .= ": page count - {$this->numPages}";
   return $base;
 }
 public function getPrice() {
   return $this->price;
 }
}
$product1 = new CdProduct("cd1", "bob", "bobbleson", 4, 50 );
print $product1->getSummaryLine()."\n";
$product2 = new BookProduct("book1", "harry", "harrelson", 4, 30 );
print $product2->getSummaryLine()."\n";
?>

输出：

cd1 ( bobbleson, bob ): playing time - 50
book1 ( harrelson, harry ): page count - 30

点评：这里进一步私有化了属性，要想获取只能通过方法。这样就确保了安全性。

希望本文所述对大家PHP程序设计有所帮助。