array Index

hi all:

 this is a portion of my code which i have in my cellImpl.

DisplayRenderer dr = display.getDisplayRenderer();
           MouseBehavior mb = dr.getMouseBehavior();
          double[] position1 = null;
          if (display instanceof DisplayImplJ3D) 
            {
             position1 = new double[] { 1.0,  1.0,  1.0};
            }
          int[] screen1 = mb.getScreenCoords(position1);
          System.out.println("screen1 = (" + screen1[0] + ", " + screen1[1]
+" " +screen1[2]+")");
        }
      }
    };
    cellfield2d.addReference(ref);

when i click the right mouse,  i get the error below

java.lang.ArrayIndexOutOfBoundsException
        at Spikesxxx$1.doAction(Spikesxxx.java:176)
        at visad.ActionImpl.run(ActionImpl.java:243)
        at visad.util.ThreadPool$ThreadMinnow.run(ThreadPool.java:95)

it seemns i am getting only 2 coordinates instead of 3. the missing one will
be the z-axis component. am i doing something wrong or missing something ?
what can possibly cause only two coordinates to be read ?

appreciate any help or workaround

thanks

Isaac