Summary of three commonly used design patterns in PHP

This article briefly introduces the three most commonly used design patterns in PHP: singleton design pattern, factory design pattern and observer design pattern. These are some personal experience summaries. I hope friends can like

Singleton Design Pattern

The so-called singleton pattern is the most commonly used in applications. Only one instance of this class exists, and once created, it remains in memory!

The singleton design pattern is often used in database class design. The singleton pattern is used to connect to the database only once to prevent multiple database connections from being opened.

A singleton class should have the following characteristics:

A singleton class cannot be directly instantiated and created, but can only be instantiated by the class itself. Therefore, to obtain such a restrictive effect, the constructor must be marked private, thus preventing the class from being instantiated.

Requires a private static member variable to save the class instance and expose a public static method that can access the instance.

In PHP, in order to prevent others from cloning singleton class instances, an empty private __clone() method is usually provided for it.

Examples of singleton pattern:

 <?php
 
/**
* Singleton of Database
*/
class Database
{
  // We need a static private variable to store a Database instance.
  privatestatic $instance;
 
  // Mark as private to prevent it from being instanced.
  privatefunction__construct()
  {
    // Do nothing.
  }
 
  privatefunction__clone() 
  {
    // Do nothing.
  }
 
  publicstatic functiongetInstance() 
  {
    if (!(self::$instanceinstanceofself)) {
      self::$instance = newself();
    }
 
    returnself::$instance;
  }
}
 
$a =Database::getInstance();
$b =Database::getInstance();
 
// true
var_dump($a === $b);

Factory design pattern

Factory design pattern is commonly used It is used to create an instance specifically used to instantiate and return its corresponding class based on different input parameters or application configuration.

Let’s take an example. Assume that rectangle and circle have the same method. Then when we use the API provided by the base class to create an instance, we will automatically create an instance of the corresponding class by passing parameters. They all have access to Functions of perimeter and area.

 <?php
 
interfaceInterfaceShape 
{
 functiongetArea();
 functiongetCircumference();
}
 
/**
* 矩形
*/
class Rectangle implementsInterfaceShape
{
  private $width;
  private $height;
  
  publicfunction__construct($width, $height)
  {
    $this->width = $width;
    $this->height = $height;
  }
 
  publicfunctiongetArea() 
  {
    return $this->width* $this->height;
  }
 
  publicfunctiongetCircumference()
  {
    return 2 * $this->width + 2 * $this->height;
  }
}
 
/**
* 圆形
*/
class Circle implementsInterfaceShape
{
  private $radius;
 
  function__construct($radius)
  {
    $this->radius = $radius;
  }
 
 
  publicfunctiongetArea() 
  {
    return M_PI * pow($this->radius, 2);
  }
 
  publicfunctiongetCircumference()
  {
    return 2 * M_PI * $this->radius;
  }
}
 
/**
* 形状工厂类
*/
class FactoryShape 
{ 
  publicstatic functioncreate()
  {
    switch (func_num_args()) {
      case1:
      return newCircle(func_get_arg(0));
      case2:
      return newRectangle(func_get_arg(0), func_get_arg(1));
      default:
        # code...
        break;
    }
  } 
}
 
$rect =FactoryShape::create(5, 5);
// object(Rectangle)#1 (2) { ["width":"Rectangle":private]=> int(5) ["height":"Rectangle":private]=> int(5) }
var_dump($rect);
echo "<br>";
 
// object(Circle)#2 (1) { ["radius":"Circle":private]=> int(4) }
$circle =FactoryShape::create(4);
var_dump($circle);

Observer design pattern

The observer pattern is a very common design pattern, and it can be used properly It brings great convenience to the program. If used improperly, it will give future generations an idea that is difficult to maintain.

What is the observer pattern? An object makes itself observable by providing methods that allow another object, an observer, to register itself). When an observable object changes, it sends messages to registered observers. These observers use this information to perform operations independent of the observable object. The result is that objects can talk to each other without having to understand why. The observer pattern is an event system, which means that this pattern allows a class to observe the state of another class. When the state of the observed class changes, the observing class can receive notifications and take corresponding actions; observation The operator pattern provides you with the ability to avoid tight coupling between components. You will understand after looking at the example below!

 <?php
 
/*
观察者接口
*/
interfaceInterfaceObserver
{
  functiononListen($sender, $args);
  functiongetObserverName();
}
 
// 可被观察者接口
interfaceInterfaceObservable
{
  functionaddObserver($observer);
  functionremoveObserver($observer_name);
}
 
// 观察者抽象类
abstractclass Observer implementsInterfaceObserver
{
  protected $observer_name;
 
  functiongetObserverName() 
  {
    return $this->observer_name;
  }
 
  functiononListen($sender, $args)
  {
 
  }
}
 
// 可被观察类
abstractclass Observable implementsInterfaceObservable 
{
  protected $observers = array();
 
  publicfunctionaddObserver($observer) 
  {
    if ($observerinstanceofInterfaceObserver) 
    {
      $this->observers[] = $observer;
    }
  }
 
  publicfunctionremoveObserver($observer_name) 
  {
    foreach ($this->observersas $index => $observer) 
    {
      if ($observer->getObserverName() === $observer_name) 
      {
        array_splice($this->observers, $index, 1);
        return;
      }
    }
  }
}
 
// 模拟一个可以被观察的类
class A extendsObservable 
{
  publicfunctionaddListener($listener) 
  {
    foreach ($this->observersas $observer) 
    {
      $observer->onListen($this, $listener);
    }
  }
}
 
// 模拟一个观察者类
class B extendsObserver 
{
  protected $observer_name = &#39;B&#39;;
 
  publicfunctiononListen($sender, $args) 
  {
    var_dump($sender);
    echo "<br>";
    var_dump($args);
    echo "<br>";
  }
}
 
// 模拟另外一个观察者类
class C extendsObserver 
{
  protected $observer_name = &#39;C&#39;;
 
  publicfunctiononListen($sender, $args) 
  {
    var_dump($sender);
    echo "<br>";
    var_dump($args);
    echo "<br>";
  }
}
 
$a = new A();
// 注入观察者
$a->addObserver(new B());
$a->addObserver(new C());
 
// 可以看到观察到的信息
$a->addListener(&#39;D&#39;);
 
// 移除观察者
$a->removeObserver(&#39;B&#39;);
 
// 打印的信息：
// object(A)#1 (1) { ["observers":protected]=> array(2) { [0]=> object(B)#2 (1) { ["observer_name":protected]=> string(1) "B" } [1]=> object(C)#3 (1) { ["observer_name":protected]=> string(1) "C" } } }
// string(1) "D"
// object(A)#1 (1) { ["observers":protected]=> array(2) { [0]=> object(B)#2 (1) { ["observer_name":protected]=> string(1) "B" } [1]=> object(C)#3 (1) { ["observer_name":protected]=> string(1) "C" } } }
// string(1) "D"

Summary: The above is the entire content of this article, I hope it will be helpful to everyone's study.

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