// Define an enum type:
enum Signal { GREEN, YELLOW, RED }

public class TrafficLight {	
	Signal color = Signal.RED;
	
	public void change() {
	    switch(color) {
	      // Note that you don't have to say Signal.RED
	      // in the case statement:
	      case RED:    color = Signal.GREEN;
	                   break;
	      case GREEN:  color = Signal.YELLOW;
	                   break;
	      case YELLOW: color = Signal.RED;
	                   break;
	    }
	}
	
	public String toString() {
	    return "The traffic light is " + color;
	}
	
	public static void main(String[] args) {
	    TrafficLight t = new TrafficLight();
	    for(int i = 0; i < 10; i++) {
	      System.out.println(t);
	      t.change();
	    }
	}
}