Chapter 16 Exercise 21, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

16.21 (Count-down stopwatch)
Write a program that allows the user to enter time in seconds
in the text field and press the Enter key to count down the seconds,
as shown in Figure 16.45d. The remaining seconds are redisplayed every
one second. When the seconds are expired, the program starts to play
music continuously.

import javafx.animation.Animation;
import javafx.animation.KeyFrame;
import javafx.animation.Timeline;
import javafx.application.Application;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.TextField;
import javafx.scene.layout.Pane;
import javafx.scene.layout.StackPane;
import javafx.scene.media.Media;
import javafx.scene.media.MediaPlayer;
import javafx.scene.text.Font;
import javafx.stage.Stage;
import javafx.util.Duration;

import java.io.File;

/**
 *
 * (Count-down stopwatch)
 *      Write a program that allows the user to enter time in seconds
 *      in the text field and press the Enter key to count down the seconds,
 *      as shown in Figure 16.45d. The remaining seconds are redisplayed every
 *      one second. When the seconds are expired, the program starts to play
 *      music continuously.
 * Created by luizsa on 9/29/14.
 */
public class Exercise_21 extends Application {

    final String URL = "home/ghosthenry/us.mp3";

    @Override
    public void start(Stage primaryStage) throws Exception {

        TextField tfCountDown = new TextField("0");
        tfCountDown.setFont(Font.font(50));
        tfCountDown.setPrefColumnCount(3);
        tfCountDown.setAlignment(Pos.CENTER);
        tfCountDown.setFocusTraversable(false);
        Pane pane = new Pane(tfCountDown);
        StackPane stackPane = new StackPane(pane);

        Timeline timeline = new Timeline(
                new KeyFrame(Duration.millis(1000), e-> {
                    tfCountDown.setText((Integer.parseInt(tfCountDown.getText()) - 1) + "");
        }));

        tfCountDown.setOnAction(e-> {
            if (timeline.getStatus() == Animation.Status.RUNNING) {
                timeline.stop();
            }
            timeline.setCycleCount(Integer.parseInt(tfCountDown.getText()));
            tfCountDown.setEditable(false);
            timeline.play();
        });

        File file = new File(URL);
        MediaPlayer mediaPlayer = new MediaPlayer(new Media(file.toURI().toString()));

        timeline.setOnFinished(event -> {
            mediaPlayer.play();
        });
        primaryStage.setScene(new Scene(stackPane));
        primaryStage.setTitle("Countdown");
        primaryStage.show();
    }

    public static void main(String[] args) {
        Application.launch(args);
    }
}