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Simple On/Off Switch

This example shows an FSM designed to control a simple switch.

We won't get into specific Actions yet since we're focused more on the FSM Diagram here, but there are lots of actions to look forward to!

FSM Diagram:


  • The START event activates the Off state.


  • The Off state performs the switch's Off Actions (E.g., turn off a light).
  • The Off state responds to one event: switchOn.
  • The switchOn event triggers a transition to the On state.


  • The On state performs the switch's On Actions (E.g., turn on a light).
  • The On state responds to one event: switchOff.
  • The switchOff event triggers a transition to the Off state.

This is rather long winded description of the FSM's behavior - once you learn to read FSM diagrams you'll find that a picture really is worth a thousand words!


Even in this simple example you can see some cool properties of state machines:

  • The states and events are plain English descriptions.
  • At a glance you can see how many states an object has.
  • You can quickly see all the events that control its behavior.

While this is great for a developer looking at this FSM, it's also great for other FSMs looking at this FSM! 

You're not just defining object behaviors but a way for objects to understand each other. 


Last modified on 3/3/2013 4:18 PM by User.

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