JAVA incompatible types: Object cannot be converted to my type

Question

I'm trying to make changes to my GUI in JavaFX by doing the work on a separate thread and returning the object required. However, after doing the work and task.setOnSucceeded() is triggered I attempt to retrieve the created object and get the error "incompatible types: Object cannot be converted to type VideoScrollPane".

I think this has something to do with raw types as it's within the listener this is happening but after looking around I couldn't find the suggestions I was looking for.

Any light that can be shed would be much appreciated.

Task task = new Task<VideoScrollPane>() {
    VideoScrollPane vsp;
    @Override protected VideoScrollPane call() {
        try {
            System.out.print("thread...");

            ExecutorService executor = Executors.newCachedThreadPool();
            Future<VideoScrollPane> future = executor.submit(new Callable<VideoScrollPane>() {
                @Override public VideoScrollPane call() {
                    return new VideoScrollPane(mediaview, vboxCentre, username, project);
                }
            });

            vsp = future.get();
        } catch(Exception exception) { System.out.println(exception.getMessage()); }

        return vsp;
    }
};
new Thread(task).start();

task.setOnSucceeded(new EventHandler<WorkerStateEvent>() {
    @Override public void handle(WorkerStateEvent t) {
        System.out.println("complete");

        try {

            //where the problem occurs
            VideoScrollPane v = task.get();     

        } catch(Exception exception) { System.out.println(exception.getMessage()); }
    }
});

Answer 1

This is because the task.get() is returning a value of type Object, but you're trying to assign it to v, which is a VideoScrollPane. You can prevent the error by doing a cast, like so

VideoScrollPane v = (VideoScrollPane)task.get();

Be warned, if task.get() returns something that isn't a VideoScrollPane, you'll get a ClassCastException.

If you want to prevent the problem entirely however, consider fixing the declaration of task, by including a type for the generic parameter. You could change it to,

Task<VideoScrollPane> task = new Task<VideoScrollPane>() {

This way, task.get() will now return a VideoScollPane, and you won't need a cast.

Answer 2

You have declared your Task incorrectly. You need

Task<VideoScrollPane> task = new Task<VideoScrollPane>() { ... }