Detailed explanation of constructors and destructors in php_PHP tutorial

In PHP, constructors and destructors are used in classes. Now I will give you a detailed introduction to the method of using constructors and destructors in PHP classes. Friends who need to know more can refer to it. .

Destructor

The role of the PHP destructor is just the opposite of the constructor. The constructor is automatically executed when the object is instantiated, while the destructor is automatically executed when the object is destroyed.

By default, PHP only releases the memory occupied by object properties and does not destroy object-related resources. Instead, it uses the destructor to execute code after using an object to clear the memory and destroy the object from memory. The structure of the destructor function __destruct() is as follows:

代码如下	复制代码
function __destruct(){     /* class initialization code */ }

The destructor is automatically called by the system and cannot take parameters.

Example:

The code is as follows

Copy code

代码如下	复制代码
class des{ function __destruct(){ echo "运行结束，执行析构函数"; } } $p=new des(); /* 实例化类 */ $sum=0; for($i=0;$i<10;$i++){ $sum=$sum+$i; echo $sum ." ";  } ?>

class des{
function __destruct(){
echo "Run ends, execute destructor";
}
}
$p=new des(); /* Instantiate class */
$sum=0;
for($i=0;$i<10;$i++){
$sum=$sum+$i;
echo $sum ."
";
}
?>

Call of destructor

How to call the destructor in PHP? The destructor is called when the php script is no longer associated with the object. If you want to explicitly destroy an object by calling the destructor, you can assign no value to the variable pointing to the object. You usually assign the variable to NULL or use the unset() function.

Example:

代码如下	复制代码
class des{ function __destruct(){ echo "对象被销毁，执行析构函数 ";   }  }  $p=new des(); /* 实例化类 */  echo "程序开始 ";  unset($p); /* 销毁变量$p */  echo "程序结束"; ?>

The code is as follows	Copy code
class des{ function __destruct(){ echo "The object is destroyed and the destructor is executed "; } } $p=new des(); /* Instantiate class */ echo "Program starts "; unset($p); /* Destroy variable $p */ echo "Program ends"; ?>

Constructor

In the process of using classes, we sometimes need to instantiate multiple fields of the object immediately. If done manually, it will bring many unpredictable problems. If it is executed automatically during the object creation process, it will bring many unpredictable problems. Comes in a lot of convenience.

The PHP constructor function is a function that is automatically executed when a class is instantiated, also called a constructor.

代码如下	复制代码
function __construct([argument1,argument2,argument3]){     /* class initialization code */ }

The declaration of the constructor is the same as other functions. The name of the knowledge constructor is the fixed name of "__construct", and its structure is as follows:

The code is as follows	Copy code
function __construct([argument1,argument2,argument3]){ /* class initialization code */ }

实例：

 代码如下

代码如下	复制代码
class user{ public $name; private $password; private $login; public function __construct($name,$password){ $this->name=$name;    $this->password=$password;    $this->login=time();   }   function getlogin(){    return(date('M d,Y',$this->login));   }  }  $user=new user('Marry','888888');  echo "用户名： ". $user->name. " ";  print("访问时间". $user->getlogin()); ?>

复制代码

 class user{
  public $name;
  private $password;
  private $login;
  public function __construct($name,$password){
   $this->name=$name;
   $this->password=$password;
   $this->login=time();
  }
  function getlogin(){
   return(date('M d,Y',$this->login));
  }
 }
 $user=new user('Marry','888888');
 echo "用户名： ". $user->name. "
";
 print("访问时间". $user->getlogin());
?>

代码如下	复制代码
class task1{   public function __construct(){    echo "today is Monday". " ";   }  }  class task2 extends task1{   function __construct(){    parent::__construct(); /* 调用父类构造函数 */    echo "I must work!";   }  }  new task2; ?>

调用父类构造函数

构造函数可以被子类调用，php调用父类构造函数时必须使用parent关键字，否则不会自动调用。

实例：

代码如下	复制代码
class task1{   public function __construct(){    echo "today is Monday". " ";   }  }  class task2 extends task1{   function __construct(){    parent::__construct(); /* 调用父类构造函数 */    echo "I must work!";   }  }  new task2; ?> http://www.bkjia.com/PHPjc/628822.html www.bkjia.comtruehttp://www.bkjia.com/PHPjc/628822.htmlTechArticle在php中构造函数与析构函数都是使用在类中的，下面我来给大家详细介绍关于在php类中使用构造函数与析构函数的方法，有需要了解的朋友...