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PHP面向对象继承用法详解(优化与减少代码重复)

2017年12月12日  | 移动技术网IT编程  | 我要评论

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。

更多关于php相关内容感兴趣的读者可查看本站专题：《php面向对象程序设计入门教程》、《php基本语法入门教程》、《php运算与运算符用法总结》、《php网络编程技巧总结》、《php数组(array)操作技巧大全》、《php字符串(string)用法总结》、《php+mysql数据库操作入门教程》及《php常见数据库操作技巧汇总》

希望本文所述对大家php程序设计有所帮助。

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