TrafficSignal class (cont.)
nadvance moves currentState to the next state.
npublic void advance () {
n private int currentState;
n if (currentState == LEFT)
n currentState = GO;
n else if (currentState == GO)
n currentState = CAUTION;
n else if (currentState == CAUTION)
n currentState = STOP;
n else //currentState == STOP
n currentState = LEFT;
n}