What is singleton design pattern? Where singleton design pattern can be applicable?

If a design requires only one instance of a particular class throughout an execution is known as singleton design pattern.

It ensures single instance of a class for the entire request life-cycle in a web application. Lets check the following code snippet of a basic singleton example in PHP:

class Logging
{
  private static $instance;
  private function __construct() {
  }

  public static function getInstance(){
    if(!isset(self::$instance)){
      self::$instance = new Logging();
    }

    return self::$instance;
  }
}
$firstObj  = Logging::getInstance();
$secondObj = Logging::getInstance();

if($firstObj === $secondObj) {
  echo 'Both objects are same';
}
else{
  echo 'Both objects are not same';
}

Output

Both objects are same

Where singleton pattern should be used?

In following situations we can use singleton pattern:

• In database configuration and connection singleton pattern can be used to keep single connection throughout the life-cycle
• For designing the logger class we can consider singleton design patter