Controlling a countdown from another Thread

Question

I'd like to implement a counter in my JavaFX application. The behavior is simply controlled via a Button:

1. When the user clicks on the button first, then the countdown starts to countdown 10, 9, 8, ..., 0
2. When the user clicks on the button during the countdown, the countdown should canceled
3. After 2. the user should be able to run the countdown again starting by 10

During the countdown, some heavy math computing is processed (on my application audio analysing).

Can you please look at my source code, if I doing it in the right way? In particular should I do the Platform.runLater stuff on the CountdownController or in the CountdownView and can I use a simple Java Thread or should I use the JavaFX Service/Task classes? Any suggestions are welcome.

The application is divided into 3 components:

1. CountdownTest: creates the Stage and start JavaFX)
2. CountdownView: singleton, contains a simple Button, passes button events to CountdownController
3. CountdownController: singleton, starts a new Thread. Within the Thread the countdown is performed, the CountdownView is updatet to show the new countdown state and some math stuff is processed.

CountdownTest.java

package org.example;

import javafx.application.Application;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.stage.Stage;

public class CountdownTest extends Application {
    @Override
    public void start(Stage primaryStage) throws Exception {
        final Group root = new Group();
        final Scene scene = new Scene(root);
        root.getChildren().setAll(CountdownView.getInstance());
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    @Override
    public void stop() throws Exception {
        super.stop();
        CountdownController.getInstance().stop();
    }

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

CountdownView.java

package org.example;

import javafx.event.EventHandler;
import javafx.scene.Group;
import javafx.scene.control.Button;
import javafx.scene.control.Tooltip;
import javafx.scene.input.MouseEvent;

public final class CountdownView extends Group {
    private static final CountdownView instance = new CountdownView();

    private Button start;

    private CountdownView() {
        start = new Button("Start");
        start.setTooltip(new Tooltip("click to start countdown"));
        start.setOnMouseClicked(new EventHandler<MouseEvent>() {
            @Override
            public void handle(MouseEvent event) {
                CountdownController.getInstance().onStartClick();
            }
        });

        this.getChildren().setAll(start);
    }

    public void startCountdown() {
        System.out.println("startCountdown");
        start.setTooltip(new Tooltip("click to stop countdown"));
    }

    public void setCountdown(final int countdown) {
        System.out.println("setCountdown " + countdown);
        start.setText(String.valueOf(countdown));
    }

    public void reset() {
        System.out.println("reset");
        start.setText("Start");
        start.setTooltip(new Tooltip("click to start countdown"));
    }

    public static CountdownView getInstance() {
        return instance;
    }
}

CountdownController.java

package org.example;

import javafx.application.Platform;

public final class CountdownController {
    private static final CountdownController instance = new CountdownController();

    private Thread countdownThread;
    private volatile boolean running = false;

    public void onStartClick() {
        if (!running) {
            countdownThread = new Thread(new Runnable() {
                @Override
                public void run() {
                    running = true;
                    int countdown = 10;
                    Platform.runLater(new Runnable() {
                        @Override
                        public void run() {
                            CountdownView.getInstance().startCountdown();
                            CountdownView.getInstance().setCountdown(10);
                        }
                    });
                    final long start = System.currentTimeMillis();
                    int lastCountdown = countdown;
                    while (!Thread.interrupted() && countdown > 0) {
                        countdown = (int) (10 - (System.currentTimeMillis() - start) / 1000);
                        if (countdown != lastCountdown) {
                            lastCountdown = countdown;
                            final int currentCountdown = countdown;
                            Platform.runLater(new Runnable() {
                                @Override
                                public void run() {
                                    CountdownView.getInstance().setCountdown(
                                            currentCountdown);
                                }
                            });
                        }

                        // Do some heavy computing stuff
                        for (int i = 0; i < 10000000; i++) {
                            Math.sin(Math.random());
                        }
                    }
                    running = false;
                    Platform.runLater(new Runnable() {
                        @Override
                        public void run() {
                            CountdownView.getInstance().reset();
                        }
                    });
                }
            });
            countdownThread.start();
        } else {
            countdownThread.interrupt();
        }
    }

    public void stop() {
        if (countdownThread != null) {
            System.out.println("stop");
            countdownThread.interrupt();
        }
    }

    public static CountdownController getInstance() {
        return instance;
    }
}

Answer 1

Don't over-sweat it. The task and service classes are just some utilities built over executors, if you don't need what they have to offer then it's just extra work.

I think you are correct in using the controller to decide which thread things should be run on, your view has enough to do routing messages between the components and the controller.