class DB { private static $_connection = null; private function __construct() { // Database connection configuration $dns = "mysql:host=localhost;dbname=mydatabase"; $username = "myusername"; $password = "mypassword"; self::$_connection = new PDO($dns, $username, $password); } public static function getConnection() { if(self::$_connection == null) { new DB(); } return self::$_connection; } }In the above code, the `DB` class has a private static property called `$_connection`. This property is assigned a value of `null` initially. The constructor of the class initializes the static property with a new `PDO` object, which creates a database connection. The `getConnection()` method is a public static method which returns the static property `$_connection`. If `$_connection` is null (no database connection has been made), it calls the `DB` constructor to create a new connection. This code example is using the PDO library in PHP. Overall, using a static _connection can improve performance and efficiency in database applications, as it allows for a single connection to be shared across all instances of a class.