public void addExit(Exit exit) {
   synchronized (exits) {
     exits.add(exit);
   }
 }
 public void addClock(TimeClock clock) {
   synchronized (clocks) {
     clocks.add(clock);
   }
 }
 public void addArea(TickArea tock) {
   synchronized (areas) {
     areas.add(tock);
   }
 }