PHP面向对象继承用法详解

这篇文章主要介绍了PHP面向对象继承用法,结合实例形式分析了php面向对象程序设计中继承的使用方法及代码优化处理与减少代码重复的相关操作技巧,需要的朋友可以参考下

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。

以上就是本文的全部内容，希望对大家的学习有所帮助。

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