Ada-Java quick question

Ada-Java quick question

[Kendal Van Dyke]

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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Re: Ada-Java quick question

[Tucker Taft]

Kendal Van Dyke (kendal@fn3.freenet.tlh.fl.us) wrote:

: 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?

What is a tankwar_obj?  If it is derived directly or indirectly
from java.awt.Component.Component_Obj then you can write:

   ... := new_mediatracker(Component_Ptr(obj));

Otherwise, you will need to pass an additional parameter to "init"
which is some derivative of Component_Obj.  Note that 
java.applet.Applet.Applet_Obj is derived from Component_Obj,
so if tankwar_obj is the applet object, then you can use that.
Ada 95 requires the explicit conversion to Component_Ptr, because
its type checking model is "stronger" than Java's for access types
(not necessarily helpfully stronger in cases like this).

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:     .                |/                       .
:     .                |\ENDAL                  .
:     . WWW   => http://www.cs.fsu.edu/~vandyke .
:     . EMail => vandyke@cs.fsu.edu             .
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-Tucker Taft   stt@inmet.com   http://www.inmet.com/~stt/
Intermetrics, Inc.  Burlington, MA  USA