Car parking - Software Development Case Studies in Java - page 293

Observer

GUIFrame

GUIMessages GUIParkingArea

update()
main()

Car TrafficLight PhotoCell Dispenser StoppingBar Controller

setGreen()
setRed()
run()

occupy()
clear()
run()

deliver()
withdraw()
run()

raise()
lower()
run()

run() run()

Figure 11.9 The GUI classes

the value of the state variable and wake up the thread. The run() method
notifies state transitions.

package parking;
public class TrafficLight extends EventProcess {
public boolean stop # false ;
// true if the light is red, false if green
String eventName;
// the name of an event that will be broadcast
public TrafficLight(String name) {
super (name);

}
// sets the state to "RED", if it is "GREEN";
// then it notifies the thread
public void setRed() {
if (stop) return ;
eventName # "RED";
stop # true ;
synchronized ( this ) { notify(); }

}
// sets the state to "GREEN", if it is "RED";
// then it notifies the thread
public void setGreen() {
if (!stop) return ;
eventName # "GREEN";
stop # false ;
synchronized ( this ) { notify(); }

}