Killer Game Programming in Java

Behaviors in Java 3D

A Behavior object is used to monitor events occurring in a Java 3D application, such as key presses, the rendering of frames, the passage of time, the movement of the user's viewpoint, Transform3D changes, and collisions. These events, called wakeup criteria, activate the Behavior object so it can carry out specified tasks.

A typical Behavior subclass has the following format:

    public class FooBehavior extends Behavior
    {
      private WakeupCondition wc;   // what will wake the object
      // other global variables

      public FooBehavior(...)
      {  // initialise globals
          wc = new ...  //  create the wakeup criteria
      }

      public void initialize()
      // register interest in the wakeup criteria
      {  wakeupOn(wc);  }


      public void processStimulus(Enumeration criteria)
      {
         WakeupCriterion wakeup;
         while (criteria.hasMoreElements() ) {
           wakeup = (WakeupCriterion) criteria.nextElement();
           // determine the type of criterion assigned to wakeup;
           // carry out the relevant task;
         }
         wakeupOn(wc);  // reregister interest
       } // end of processStimulus()

    }  // end of FooBehavior class

A subclass of Behavior must implement initialize() and processStimulus(). initialize() should register the behavior's wakeup criteria, but other initialization code can be placed in the constructor for the class. processStimulus() is called by Java 3D when an event (or events) of interest to the behavior is received. Often, processStimulus() being called is enough to decide what task should be carried out, e.g., TimeBehavior. In more complex ...