In addition to KeyValue, KeyFrame allows us to set a handler which will trigger at the selected Duration. For example, in the preceding timeline, we can change the object color in the middle:

KeyFrame keyFrame = new KeyFrame(Duration.seconds(5), 
            (ActionEvent event) -> {
                circle.setFill(Color.GREEN);
            },
            new KeyValue(circle.translateXProperty(), 200));
KeyFrame keyFrame2 = new KeyFrame(Duration.seconds(10), 
            new KeyValue(circle.translateYProperty(), 200));
Timeline timeline = new Timeline(keyFrame, keyFrame2);

This allows us to make simple timers for events on a UI thread:

Timeline timer = new Timeline(new KeyFrame(Duration.seconds(1), 
    (event) -> {
        System.out.println("every second on the UI thread");
})); // no keyvalues is ok

timer.setCycleCount(Timeline.INDEFINITE);
timer.play();