Java Code. Алексей Алексеевич Крючков

fadeInKey1 = new KeyFrame(Duration.millis(500), new KeyValue (toastStage.getScene().getRoot().opacityProperty(), 1));

              tl1.getKeyFrames().add(fadeInKey1);   

              tl1.setOnFinished((ae) ->

              {

                  new Thread(() -> {

                      try

                      {

                          Thread.sleep(2000);

                      }

                      catch (InterruptedException e)

                      {

                          e.getMessage();

                      }

                         Timeline tl2 = new Timeline();

                          KeyFrame fadeOutKey1 = new KeyFrame(Duration.millis(500), new KeyValue (toastStage.getScene().getRoot().opacityProperty(), 0));

                          tl2.getKeyFrames().add(fadeOutKey1);   

                          tl2.setOnFinished((aeb) -> toastStage.close());

                          tl2.play();

                  }).start();

              });

              tl1.play();

          }

      Генератор арифметического примера

       String arithSchema1(){

              int a,b,c,d;

              Random random=new Random();