How is a static class or call to a static function presented in Sequence Diagram? As per my understanding, the lifeline belongs to an instance/object of a class. This article says metaclass stereotype can be used.
"In case of doubt, use comments, or stereotypes..."
Sequence Diagram:
+-------------+ +-------------------+
| <<class>> | | <<class>> |
| Cat | | FastFoodTerminal |
+------+------+ +---------+---------+
| |
| <<static>> |
| TurnOn() |
+--------------------------->+---+
| | |
+<---------------------------+<--+
| |
| Answer = |
| DoYouHaveCheeseBurger() |
+--------------------------->+---+
| | |
+<---------------------------+<--+
| |
Class Diagram:
+-------------------------------------------------+
| <<class>> |
| FastFoodTerminal |
+-------------------------------------------------+
| [+] void: FastFoodTerminal(); <<constructor>> |
| [#] int: ObtainMoneyDifference(); |
| [+] void: ReceiveMoney(); |
| [+] void: ReturnChange(); |
| [+] FastFoodTerminal: TurnOn(); <<static>> |
+-------------------------------------------------+
In this example, the "TurnOn()" is an static method that returns, an instance (object) of the "FastFoodTerminal" class.