Ada-Java quick question

[Kendal Van Dyke <kendal@fn3.freenet.tlh.fl.us>]

I'm working on an applet where I'd like to use a media tracker prevent
the applet from starting until all the images have been loaded, but I am
running into a slight problem. I don't quite know how to call
new_MediaTracker. Here's the code I have:

  procedure init(obj : access tankwar_obj) is

    tracker : mediatracker_ptr := new_mediatracker([something]);

  begin
    ...some code here.....
  end init;

According to the Ada-Java API [something] has to be of type
component_ptr. In regular Java, it's usually called as 
"new MediaTracker(this)". I know that in most cases in Ada-Java you can
use "null" in place of "this" and it will work, but it didn't in this
case. So, in this code, what would I use to fill in the [something]
part?
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