public class 类名 extends Application{
    @Override
    public void start(Stage primaryStage) throws Exception {
}

//设置实时时间
        Label time = new Label();  //设置标签
        time.setFont(new Font(20));  //设置标签字体
        DateFormat currentTime = new SimpleDateFormat("yyyy.MM.dd hh:mm:ss"); //设置时间格式
        EventHandler<ActionEvent> eventHandler = e->{
            time.setText(currentTime.format(new Date()));
            System.out.println(currentTime.format(new Date()));
        };
        Timeline animation = new Timeline(new KeyFrame(Duration.millis(1000),   (javafx.event.EventHandler<ActionEvent>) eventHandler));    //一秒刷新一次
        animation.setCycleCount(Timeline.INDEFINITE);