PHP中如何实现继承

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具体如下：

继承

先看两个类

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

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

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

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

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

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

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