When this PHP code is run, the username 'superman' does not show, why?

$obj = new User('superman');

echo $obj->username;

class User{

public $username;

function __construct($param){

$username = $param;

}

}

1. The variable $username in the constructor is not calling the $username in the class (outside the constructor)

2. Cannot create an object of class User

3. Who cares?

4. username for class User is a static variable