PHP singleton mode entry example

class mysql{
 privete static $instance ;//Save the instance
 //The constructor is declared as private to prevent direct creation of objects
 privete function __construct(){
 //Instantiation
 }
 //Single case method, determine whether it has been instantiated, and only instantiate it once
 public static function getInstance (){
 if(!isset( self::$instance )){
 self ::$instance = new self();
 }
 return self:: $instance;
 }
 //Prevent cloning objects
 private function __clone (){
 trigger_error ("not allow to clone.");
 }
 function test(){
 echo "test" ;
 }
}
$conn = mysql::getInstance ();
$conn->test ();
?>