Killer Game Programming in Java

Updating the Alien Sprite

TimeBehavior acts as a Timer-like object for calling the update() method in AlienSprite every 500 milliseconds. The two are linked together by WrapTour3D in its addAlien() method:

    private void addAlien()
    {
      AlienSprite al =  new AlienSprite("hand1.obj", obs, bob);   // alien
      al.setPosition(-6.0, -6.0);
      sceneBG.addChild( al.getTG() );

      TimeBehavior alienTimer = new TimeBehavior(500, al);  // alien's controls
      alienTimer.setSchedulingBounds( bounds );
      sceneBG.addChild( alienTimer );
    }

The TimeBehavior class is simpler than TouristControls since its processStimulus() method being called is enough to trigger the call to update():

    public class TimeBehavior extends Behavior
    {
      private WakeupCondition timeOut;
      private AlienSprite alien;

      public TimeBehavior(int timeDelay, AlienSprite as)
      { alien = as;
        timeOut = new WakeupOnElapsedTime(timeDelay);
      }

      public void initialize()
      { wakeupOn( timeOut );  }


      public void processStimulus( Enumeration criteria )
      { alien.update();      // ignore criteria
        wakeupOn( timeOut ); // re-register
      }
    }

The wakeup criterion is an instance of WakeupOnElapsedTime.