问JavaFX，Platform.runlater()有回调吗？

EN

public class UpdateHandler {
     private final AtomicInteger count;
     private final Runnable completionHandler;

     public UpdateHandler(Runnable completionHandler, Runnable... initialTasks) {
         if (completionHandler == null || Stream.of(initialTasks).anyMatch(Objects::isNull)) {
             throw new IllegalArgumentException();
         }
         count = new AtomicInteger(initialTasks.length);
         this.completionHandler = completionHandler;
         for (Runnable r : initialTasks) {
             startTask(r);
         }
     }

     private void startTask(Runnable runnable) {
         Platform.runLater(() -> {
             runnable.run();
             if (count.decrementAndGet() == 0) {
                 completionHandler.run();
             }
         });
     }

     public void Runnable runLater(Runnable runnable) {
         if (runnable == null) {
             throw new IllegalArgumentException();
         }
         count.incrementAndGet();
         startTask(runnable);
     }

}