PHP singleton mode implementation (object is only created once)_PHP tutorial

A singleton class has at least the following three public elements:

Must have a constructor and must be marked private.
Has a static member variable that holds an instance of the class.
Has a public static method that accesses this instance

In terms of specific usage, I have clearly commented in the php example below:

Copy the code The code is as follows:

/**
  * by www.phpddt.com
 */
class Mysql{
//This attribute is used to save the instance
private static $conn;
//The constructor is private, Prevent object creation
private function __construct(){
$this->conn = mysql_connect('localhost','root','');
}
//Create an instance Object method
public static function getInstance(){
if(!(self::$conn instanceof self)){
self::$conn = new self;
}
return self::$conn;
}
//Prevent the object from being copied
public function __clone(){
trigger_error('Clone is not allowed!');
}

}
//You can only get the instance in this way, not new and clone
$mysql = Mysql::getInstance();
?>

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