Car parking - Software Development Case Studies in Java - page 290

TrafficLight PhotoCell TicketDispenser StoppingBar

GREEN CLEARED DELIVERED DOWN

setRed()
RED

setGreen()
GREEN

occupy()
OCCUPIED

clear()
CLEARED

withdrawn()
WITHDRAWN

deliver()
DELIVERED

raise()
UP

lower()
DOWN

RED OCCUPIED WITHDRAWN UP

Figure 11.4 Finite state automata of traffic light, photocell, ticket dispenser and stopping bar

upper label indicates the condition that triggers the transition. For example,
occupy() is the method of PhotoCell that triggers the transition from CLEARED
to OCCUPIED . The lower label indicates the action that is performed during
state transition. For example, PhotoCell notifies event OCCUPIED . Event
names are in italic upper case.
Figure 11.5 depicts the controller's finite state automaton. It is made up of
eight states that represent the phases described in Section 11.1.3.
Figure 11.6 depicts the car's finite state automaton. For the sake of
simplicity, we assume that only one car is present in the system at any time;
that is, in this prototype we do not model the queue of waiting cars.

IN_PhC.
CLEARED
SEM.setRed()
TD.deliver()

IN_PhC.
OCCUPIED

TD.DELIVERED

PHASE 1 PHASE 2 PHASE 3 PHASE 4

TD.
WITHDRAWN

SB.DOWN

SEM.setGeen()

SB.raise()

PHASE 8 PHASE 7 PHASE 6 PHASE 5

OUT_PhC.
CLEARED
SB.lower()

OUT_PhC.
OCCUPIED

SB.UP

Figure 11.5 Finite state automaton of controller