Detailed explanation of object-oriented inheritance usage in PHP (optimizing and reducing code duplication)

The examples in this article describe the use of object-oriented inheritance in PHP. Share it with everyone for your reference, the details are as follows:

Inheritance

Look at the two classes first

<?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";
?>

Output:

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

Comments: The codes of these two categories are too repetitive, with similarities and differences. It's better to use inheritance to simplify the process.

Use inheritance to process

<?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";
?>

Output:

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

Comments: Inheritance processing solves the problem of differences and compatibility very well.

Further optimization processing

<?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";
?>

Output:

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

Comments: Here, the common attributes are placed in the parent class, and other individual attributes are handled in their own classes. And set your own construction method and inherit the construction method of the parent class.

Further inherited methods from the parent class

<?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";
?>

Output:

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

Comment: The same result can be optimized and optimized again. Here the methods of the parent class are inherited. parent::getSummaryLine(). However, this is used less frequently.

Continue to add some interesting content

<?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";
?>

Output:

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

Comments: The parent class added a discount. After book inherited it, the getPrice method was modified, so the discount is invalid for book.

Private properties, set and get through methods

<?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";
?>

Output:

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

Comments: The attributes are further privatized here, and can only be obtained through methods. This ensures safety.

I hope this article will be helpful to everyone in PHP programming.

For more detailed explanations of PHP object-oriented inheritance usage (optimization and reduction of code duplication), please pay attention to the PHP Chinese website!