urse of the state machine activity, there are usually several points 
  at which the machine needs to alert other objects in the environment about some 
  meaningful event that has occurred in the state machine process. The developer 
  uses <font face="Courier New, Courier, mono">notifyListener()</font> to generate 
  those events. Other objects can register to listen for all events generated 
  by this machine by using <font face="Courier New, Courier, mono">addListener()</font>. 
  There can be a theoret