PHP design pattern four: inheritance php shopping cart design php security mode php design report

data-id="1190000004994154" data-licence="">

Original address: PHP Design Patterns (4): Inheritance

Introduction

in PHP Design Patterns (2): Abstract Classes and Interfaces and PHP Design Patterns ( 3): In encapsulation, we have already seen inheritance, which is the extends keyword.
Like C/C++, Java, Python and other languages, PHP also supports inheritance, and it is no different from other languages.

Inheritance

Let’s use animals, whales and carps as examples:

<code><?php
abstract class Animal {
  protected $name;

  protected function chew($food) {
    echo $this->name . " is chewing " . $food . ".\n";
  }
  protected function digest($food) {
    echo $this->name . " is digesting " . $food . ".\n";
  }
}

class Whale extends Animal {
  public function __construct() {
    $this->name = "Whale";
  }
  public function eat($food) {
    $this->chew($food);
    $this->digest($food);
  }
}

class Carp extends Animal {
  public function __construct() {
    $this->name = "Carp";
  }
  public function eat($food) {
    $this->chew($food);
    $this->digest($food);
  }
}

$whale = new Whale();
$whale->eat("fish");
$carp = new Carp();
$carp->eat("moss");
?></code>

Run it:

<code>$ php Inheritance.php
Whale is chewing fish.
Whale is digesting fish.
Carp is chewing moss.
Carp is digesting moss.</code>

Pay attention to the usage of $this in the Animal class, Whale class, and Carp class.
The above code seems common, but in fact it contains a mystery. For a good program design, it is necessary: ​​

1. There should be low coupling between classes.

2. Inheritance usually inherits from abstract classes rather than concrete classes.

3. Usually the concrete class that directly inherits the abstract class has only one layer, and is qualified by protected in the abstract class.

Summary

Reasonable inheritance is also essential for good programming. Combining abstract and protected allows you to write code with a clear structure.

The above introduces PHP design pattern four: inheritance, including design patterns and PHP content. I hope it will be helpful to friends who are interested in PHP tutorials.