What is Singleton Design Pattern?
Singleton pattern is a technique to provide a class global state. Once we have created the instance of the class we can use the existing instance multiple times. So it restricts the multiple instantiation of a class.It is a great example of re-usability in Object Oriented Programming System.
How it works?
We restrict the constructor while declaring it as private , of the class to access it from outside and a static method is created that returns the instance.
Example in PHP:
<?php
class SingletonClass {
private static $the_instance = null;
//the private constructor
private function __construct()
{
}
//public static function to return the instance
public static function getInstance()
{
if (self::$the_instance == null)
{
self::$the_instance = new SingletonClass();
}
return self::$the_instance;
}
}
?>
Usage of Singleton Class:
Connecting A database and use exiting connection, to avoid multiple open connection issue:
<?php
class DB {
private static $instance = null;
private $conn;
private $host = 'localhost';
private $user = 'root';
private $pass = 'password';
private $name = 'my_database_name';
private function __construct()
{
$this->conn = new PDO("mysql:host={$this->host};
dbname={$this->name}", $this->user,$this->pass,
array(PDO::MYSQL_ATTR_INIT_COMMAND => "SET NAMES 'utf8'"));
}
public static function getInstance()
{
if(!self::$instance)
{
self::$instance = new DB();
}
return self::$instance;
}
public function dbConnection()
{
return $this->conn;
}
}
?>
Now creating an Instance using the static method:
<?php $the_instance = DB::getInstance(); $conn = $the_instance->getConnection(); ?>