Question

I have the following code:

if(prevPoint != null){
            Log.i("tracking class", "prevPoint:  "+ prevPoint);
          Point pointb = null;
          Projection projection2 = mapView.getProjection();
          projection2.toPixels(prevPoint, pointb);

          Log.i("tracking class", "Pointb:  "+ pointb);
               Paint paint;
                 paint = new Paint();
                 paint.setColor(Color.BLUE);
                 paint.setAntiAlias(true);
                 paint.setStyle(Style.STROKE);
                 paint.setStrokeWidth(2);
    Log.i("tracking class", "Point x:  "+ point.x);
    Log.i("tracking class", "Point y:  "+ point.y);
    Log.i("tracking class", "Pointb x:  "+ pointb.x);
    Log.i("tracking class", "Pointb y:  "+ pointb.y);


            //canvas.drawLine(pointb.x, pointb.y, point.x, point.y, paint);
        }

The log returns this:

10-19 08:55:25.505: INFO/tracking class(29970): prevPoint:  41310173,-105558377
10-19 08:55:25.505: INFO/tracking class(29970): Pointb:  null

Any thoughts why Pointb is coming back null?

Answer 1

Are you expecting Java to use pass by reference? It doesn’t. It uses pass by value everywhere, although the value of any expression of a reference type is a reference.

Calling

projection2.toPixels(prevPoint, pointb);

cannot possibly change the value of pointb. You’ll need to use an assignment operator, e.g.

Point pointb = projection2.toPixels(prevPoint, null);

I believe toPixels changes the content of the existing object referred to by the argument, if the argument is non-null… but it can’t possibly change the value of the variable to refer to a new object.