JAVA 不兼容类型:对象无法转换为我的类型 [英] JAVA incompatible types: Object cannot be converted to my type

问题描述

我正在尝试通过在单独的线程上进行工作并返回所需的对象来更改 JavaFX 中的 GUI.但是，在完成工作并触发 task.setOnSucceeded() 后，我尝试检索创建的对象并收到错误类型不兼容:对象无法转换为 VideoScrollPane 类型".

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".

我认为这与原始类型有关，因为它在侦听器中正在发生，但环顾四周后我找不到我正在寻找的建议.

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.

任何可以发出的光都将不胜感激.

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()); }
    }
});

推荐答案

这是因为 task.get() 正在返回 Object 类型的值，但是你'正在尝试将它分配给 v，这是一个 VideoScrollPane.您可以通过执行强制转换来防止错误，就像这样

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();

请注意，如果 task.get() 返回的内容不是 VideoScrollPane，您将收到 ClassCastException.

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

但是，如果您想完全避免该问题，请考虑修复 task 的声明，通过包含泛型参数的类型.你可以把它改成，

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>() {

这样，task.get() 现在将返回一个 VideoScollPane，并且您不需要演员表.

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

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