Re: Movie() throws Exception?

Subject: Re: Movie() throws Exception?

From: Chris Adamson <email@hidden>

Date: Sun, 17 Jul 2005 19:33:54 -0400

Delivered-to: email@hidden

On Jul 17, 2005, at 4:44 PM, Elliotte Harold wrote:

I notice that the no-args Movie() constructor is declared to throw a QTException. Any idea why? i.e. in what circumstances would

Movie m = new Movie();

fail?

Among others, if you try the above without initializing QuickTime via QTSession.open():

import quicktime.*;

import quicktime.std.movies.*;

public class TrivialQTCrash {

public static void main (String[] arrrImAPirate) {

try {

new Movie(); // die die die

} catch (QTException qte) {

qte.printStackTrace();

}

produces:

[chrisg5:~/dev/experiments/trivialqtcrash] cadamson% java TrivialQTCrash

Exception in thread "main" java.lang.ExceptionInInitializerError

at quicktime.std.movies.Movie.allocate(Movie.java:394)

at quicktime.std.movies.Movie.<init>(Movie.java:384)

at quicktime.std.movies.Movie.<init>(Movie.java:372)

at TrivialQTCrash.main(TrivialQTCrash.java:8)

Caused by: quicktime.QTNullPointerException: QuickTime MUST be initialized:quicktime.qd.QDGraphics

at quicktime.QTObject._ID(QTObject.java:75)

at quicktime.qd.QDGraphics.isOffscreen(QDGraphics.java:482)

at quicktime.qd.QDGraphics.<init>(QDGraphics.java:333)

at quicktime.qd.QDGraphics.<init>(QDGraphics.java:427)

at quicktime.qd.QDGraphics.<clinit>(QDGraphics.java:56)

... 4 more

[chrisg5:~/dev/experiments/trivialqtcrash] cadamson%

Generally speaking, the Movie constructor throws an exception if the native NewMovie function returns NIL. From the native docs:

function result
The identifier for the new movie. If NewMovie fails, the returned identifier is set to NIL. You can use GetMoviesError to obtain the error result, or noErr if there was no error. See Error Codes.

The genericized QTException-throwing seen throughout QTJ represents a wrapping of the handling of return values (the classic "if err != noErr" you see in QT sample code) and lookup of error codes.

If it seems weird that you have to catch QTException on pretty much any QTJ call, just imagine if you had to catch all the RuntimeExceptions in Java. My point being that in theory, almost any call can potentially error (e.g., illegal access, out of memory, stack-heap collision), and this is more visible in native QT than it is in Java. Maybe QTJ is more of a QT mindset than a Java mindset in this regard..

--Chris

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References:

>Movie() throws Exception? (From: Elliotte Harold <email@hidden>)