import ch.aplu.nxt.*;
public class exemple
{
  public exemple()
  {
    NxtRobot monrobot = new NxtRobot(); 
    LightSensor ls = new LightSensor(SensorPort.S3);
    monrobot.addPart(ls);
    ls.activate(true);
    Gear gear = new Gear();
    gear.setSpeed(30);
    monrobot.addPart(gear);
   
 while (true)
    {
      int lum = ls.getValue();

      if (lum < 500)      {
        gear.backward(1000);
      }
    }
  }

  public static void main(String[] args)

  {
    new exemple();
 }

  // ------------------ Environment --------------------------
  static
  {
    NxtContext.setStartPosition(0, 0);
    NxtContext.setStartDirection(90);
    NxtContext.useBackground("http://www2.cstrois-lacs.qc.ca/chenebleu/informatique/ladifference/k2.gif");
  }
}